Objective lens, electron beam system and method of inspecting defect

ABSTRACT

An electron beam system or a method for manufacturing a device using the electron beam system in which an electron beam can be irradiated at a high current density and a ratio of transmittance of a secondary electron beam of an image projecting optical system can be improved and which can be compact in size. The surface of the sample S is divided into plural stripe regions which in turn are divided into rectangle-shaped main fields. The main field is further divided into plural square-shaped subfields. The irradiation with the electron beams and the formation of a two-dimensional image are repeated in a unit of the subfields. A magnetic gap formed by the inner and outer magnetic poles of the objective lens is formed on the side of the sample, and an outer side surface and an inner side surface of each of the inner magnetic pole and the outer magnetic pole, respectively, forming the magnetic gap have each part of a conical shape with a convex having an angle of 45° or greater with respect to the optical axis.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 11/136,668,filed May 25, 2005, which is based upon and claims the benefit ofpriority from the prior Japanese Patent Application No. 2004-156386,filed May 26, 2004, Japanese Patent Application No. 2004-169675, filedJun. 8, 2004, Japanese Patent Application No. 2004-192654, filed Jun.30, 2004 and Japanese Patent Application No. 2004-192655, filed Jun. 30,2004, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a high throughput apparatus forevaluating a sample having a pattern with a minimum line width of 0.1 μmor less including, for example, a pattern on a substrate, a method forthe evaluation of a pattern thereon and an objective lens for using thesame.

The present invention also relates to an electron beam system and amethod for the manufacturing of a device by using the same and, moreparticularly, to a apparatus for evaluating a sample including, but notbeing limited to a patterned wafer, a mask for forming a pattern, asubstrate for use with a liquid crystal panel or a micromachine product,etc. with both a high precision and a high throughput and to a methodfor manufacturing a device by using the electron beam system.

The present invention further relates to a method for evaluatingincluding inspecting etc. a defect on a sample having a pattern with aminimum line width of 0.2 μm or less with a high throughput and to amethod for manufacturing a device by using the same.

Moreover, the present invention relates to a method for the formation ofa pattern including, for example, IC pattern, etc. directly on a waferor the like, a method for the formation of a pattern having a minimumline width of 0.1 μm or less by means of an electron beam delineatingmethod and to a method for the repair of a mask to be used in alithography for forming a pattern having a minimum line width of 0.1 μmor less. More particularly, the present invention further relates to amethod for manufacturing a device by using the pattern-delineatingmethod and to a method for manufacturing a device by using the maskrepaired by the above method.

RELATED ART

Heretofore, there has been known an electron beam system for theevaluation of a pattern by irradiating a patterned wafer (a sample) withelectron beams. Such an electron beam system is arranged in such amanner that a wafer surface is divided virtually into plural striperegions and each stripe region is irradiated with electron beams as aunit for evaluation of the patterns formed on the wafer. The electronbeams for use in this evaluation are arranged in a rectangular shape inwhich the longitudinal length of the electron beams corresponds to thewidth of the stripe region. The rectangular electron beams are furtherarranged such that they are continually moved longitudinally along thestripe region and the full area of the stripe region is irradiated withthe electron beams. Upon irradiation of the wafer surface with theelectron beams, secondary electrons are emitted from the wafer surfaceso that a two-dimensional image of the pattern on the wafer can beformed by convergence of the secondary electrons.

Concerning the present invention 3-1, a method has been proposed inwhich a pattern is evaluated by using a plurality of electron beams,that is, multiple beams. This method, however, has not yet been madecommercially available. Moreover, no report has been found thatdescribes a way of observing multiple beams and evaluating a pattern byusing the multiple beams.

Regarding the present invention 3-2, a method has hitherto been proposedin which approximately eight electron beams are positioned at equalseparation from the optical axis, etc. to scan a surface of a sample andevaluate the sample by magnifying secondary electrons emitted from thesample by means of an image projecting an optical system. In order toarrange multiple beams at equal separation from the optical axis,however, it is necessary to locate the beams on the circumference withthe optical axis centered. Moreover, problems have become apparent inthe case of arrangement for ten or more beams, namely, a large diameteris required for the arrangement of the multiple beams and a great burdenis imposed on an electron gun causing a lens aberration.

In respect of the present invention 3-3, there have hitherto beenproposed some types of pattern evaluation apparatuses which use multiplebeams. Such conventional multiple beam systems, however, have theproblems that resolution of the beams located apart from the opticalaxis are decreased due to aberration of lenses including not only anobjective lens but also a reducing lens and a condenser lens if thenumber of beams is increased.

In respect of the present invention 4-1, the method for delineating apattern directly on a wafer (the directly delineating method) includesconventional methods in which a beam energy of 50 keV or higher isutilized and in which a beam energy of 5 keV or lesser is utilized. Thedirectly delineating method using an accelerating voltage of 50 keV orhigher has the problems that a vastly large-scale apparatus is requiredand a cost-of-owner (COO) may become too large due to a low throughput.On the other hand, the directly delineating method using the beam energyof 5 keV or lesser have the problem that an edge roughness increases,although it has the merits that a resist is highly sensitive so that thenumber of irradiating electrons per unit area becomes smaller.

Regarding the present invention 4-2, a method has been proposed in whicha boundary of main fields, subfields or stripes is made in a roughenedand uneven fashion in order to improve precision of connecting aprojection apparatus. Further, a method has been proposed in which asloping connection is effected in order to improve a precision ofconnecting a projection apparatus. Likewise, a method has further beenproposed in which an electron gun is preferably operated underspace-charge limit conditions in order to reduce an edge roughness of aprojection apparatus.

For the projection apparatus using electron beams, all patterns to beformed on a sample are needed to be formed on a mask so that anexpensive mask has to be used. Furthermore, the projection apparatus hasthe problem that a throughput is greatly reduced compared to ArFlithography or F₂ lithography.

In respect of the present invention 4-3, there is known a repairapparatus in which a mask is repaired by spraying a reactive gas onto amask surface which is irradiated with electron beams from

a nozzle disposed in a scanning electron microscope (SEM).

For the repair apparatus, a detection means for detecting the completionof repair is not sufficient. In other words, a conventional detectionmeans has the problems that, in the course of obtaining an SEM image byscanning a region wider than a sharpening portion in order to observewhether the repair has been finished or not, a region which is notsought to be shaped is also scraped off by scanning, rendering achromium layer thinner or chromium become deposited on a transparentregion in a thin layer.

SUMMARY OF THE INVENTION

Upon conducting an evaluation of a pattern formed on a substrate byusing an electron beam system, an objective lens has hitherto been usedfor focusing electron beams on a sample and forming an image thereof onthe sample surface. As the objective lens, an electromagnetic lens beenconventionally used which has a magnetic gap formed on the side of thesample with an inner electrode on the side of the optical axis and anouter electrode opposite thereto. The objective lens, however, has theproblem that a number of ampere turns (ATs) needed for operating lensesbecomes larger. Further, the objective lens presents the problem that adistribution of an axial magnetic distribution cannot be obtained at anecessary level for the reasons that a magnetic flux density within amagnetic pole becomes too large due to a remote distance between theposition of the magnetic gap and the position of the beam passingtherethrough, thereby saturating a magnetic permeability of a magneticmaterial and as a result gaining no necessary distribution of the axialmagnetic field. Therefore, the present invention has the object ofproviding an objective lens which does not make a number of ATs of anexciting current for obtaining focusing conditions larger and making amagnetic flux density of the magnetic pole higher.

Further, in the event that the magnetic lens is used as the objectivelens regardless of its aberration coefficient being smaller than anelectrostatic lens, electrons emitted from the sample surface in adirection of the normal of the sample do not cross the optical axisthereof when they are condensed with the objective lens. Therefore, themagnetic lens has the problem that no NA aperture can be disposed at thecross-over position so that no image having a high resolution can beobtained. In other words, the problem resides in that, in the eventwhere the NA aperture is disposed at the cross-over position, electronscoming from a position apart from the optical axis is blocked to anextent more than needed, thereby darkening an image at the neighboringportion. Therefore, the present invention has another object ofdecreasing aberration by using a magnetic lens as the objective lens,forming a cross-over on the optical axis and mounting an NA aperture atthe cross-over position.

An electrostatic lens has been used for an objective lens in aconventional optical system in order to improve a throughput, which isarranged so as to project secondary electrons emitted from a sample ontoa detector by forming multiple beams and scanning the sample therewith.Therefore, such a conventional system has suffered from the problem ofaberration becoming large and as a result a large beam current cannot beobtained when the beams are narrowed down to a smaller size. The presentinvention has the object, accordingly, to provide an objective lens thatcomprises a magnetic lens having a lens gap on the sample side, whichcan narrow down the multiple beams to a smaller size and obtain a largebeam current.

Moreover, if a magnetic field exists on a sample, beams coming outvertically from the sample do not cross the optical axis so that no NAaperture can be disposed and that, as a result, a crosstalk between asecondary beam and the adjacent beam becomes large. Therefore, thepresent invention has the object of providing an image with a highprecision by making such a crosstalk between the adjacent beams.

Moreover, a conventional method arranges multiple beams such thatresolution is improved by narrowing a beam size of a primary beam downto a smaller beam size. The conventional method has the defect, however,that narrowing the beam size down makes a beam current smaller inproportion to the fourth power of the beam size so that a longerduration of time is required to obtain a signal having a better S/Nratio. Therefore, the present invention has the object of providing animage having a higher resolution by using a large beam size of a primarybeam as it is and improving the resolution of a secondary opticalsystem.

In carrying out a conventional inspection for detecting a defect of asample by irradiating a sample with electron beams and forming orfocusing an image of the electron beams generated or reflected from thesample on a detector surface with an optical system, the defectdetection has been effected by dividing an entire die as an inspectionobject into stripes, each having an equal width and conducting acomparison of an image to be inspected with a reference image for eachstripe. This defect detection technique presented the problem, however,that, in the event where the die is divided into equally wide stripes inits entirety, each main field (in an x-dimensionally scanning direction)of each stripe is composed of a mixture of a region where the inspectionhas to be done by a die-to-die comparison and a region where theinspection has to be done by a cell-to-cell comparison. For this reason,a circuit for carrying out a die-to-die comparison and a circuit forcarrying out a cell-to-cell comparison have to be shifted within onemain field. These shift operations are difficult to carry out.Therefore, the present invention has the object of providing aninspection method that does not require any shift operations to becarried out within one main field.

In addition, the conventional electron beam system had the followingproblems. An electron beam applied to the conventional electron beamsystem is in a rectangular form; however, such a rectangular electronbeam cannot be used for irradiation at a high current density when theelectron beam in the rectangular form is set so as to have a constantcurrent density as a whole. Further, for the conventional electron beamsystem, electron beams distant from the optical axis are also used sothat aberration is magnified. In order to sustain aberration within aconstant scope, it is needed to make an angle of an aperture smaller. Asa result, a permeability ratio of secondary electrons of an imageprojecting optical system (a secondary optical system) becomes reduced.Moreover, although the length of the optical system can be elongated inorder to reduce aberration, the problem may be caused to occur such thatit may result in an increase in a space charge effect and so on. Thepermeability ratio of the secondary electrons for the image projectingoptical system referred to herein is intended to mean a ratio of anamount of the secondary electrons coming into the surface of ascintillator coated on an FOP with respect to an amount of the secondaryelectrons generating from a sample.

The present invention 2-1 has an object of solving the problems involvedin the conventional electron beam apparatuses and, more particularly, toprovide an electron beam system that can realize an irradiation of thesample with electron beams having a high current density, improve adetection yield of secondary electrons of an image projecting opticalsystem and further making an electron optical lens barrel compact and toprovide a method for manufacturing a device using the same.

The present invention 3-1 has been made with the above-describedproblems taken into account and has an object of providing a patternevaluation method in which weight is given to a method for adjustingmultiple beams and to provide a method for manufacturing a device with ahigh yield rate by using the pattern evaluation method.

The present invention 3-2 has been made by overcoming theabove-described problems and has an object of providing a patternevaluation method for evaluating a sample with a high throughput bygenerating ten or more multiple beams and scanning the sample with themultiple beams and, further, to provide a device production method forthe production of a device with a high yield rate by using the same.

The present invention 3-3 has been made by taking the above-describedproblems into account and has an object of providing a beam formationmethod for forming a beam which enables a beam to separate from anoptical axis by some distance to be formed on a sample in a minimallynarrowed form and which can focus a primary beam concurrently with asecondary beam.

The present invention 4-1 has been made by paying attention to theabove-described problems and has an object of providing a method fordrawing a pattern which enables turning on and off the irradiation ofelectron beams at a high speed or shifting dimensions of a variablysharpening beam or characters of character masks at a high speed andfurther which can pass through a monolayer resist on a wafer over theentire thickness and provide an electron beam with energy high enough tosensitize the resist and, further, to provide a device production methodfor the production of a device with a high yield rate by using the same.

The present invention 4-2 has been made with the above-describedproblems taken into account and has an object of providing apattern-delineating method for the formation of a pattern which can forma pattern in a substantially mask-free manner and which can connectstripes in an appropriate way simply by forming only patterns occurringfrequently in a repetitive way with a mask, and a method for forming apattern having a good edge roughness. The present invention furtherprovides a device production method for the production of a device byusing the same.

The present invention 4-3 has been made with the above-describedproblems taken into account and has an object of providing a repairmethod for repairing a pattern which does not cause a deletion of anunnecessary pattern or deposition of chromium during a course ofinspection concerning whether the repair has been completed or not. Thepresent invention further provides a device production method for theproduction of a device by using a mask repaired by the repair method.

In order to achieve the above-described objects, the present invention1-1 provides an objective lens that can focus electron beams on asample, which comprises a magnetic gap formed by an inner magnetic polelocated on the side of an optical axis and an outer magnetic polelocated on the side opposite thereto is formed on the side of thesample, at least one side of the outer side and the inner side of theinner magnetic pole and the outer magnetic pole, respectively, whichforms the magnetic gap, constitutes part of a conical shape having avertical angle at which an angle respect to the optical axis is 45° orlarger and a cross section of each of the magnetic poles in the vicinityof the sample has an angle of 90° or larger.

In accordance with the present invention 1-2, the electron beam systemcomprises an electron gun, an irradiation optical system, a samplecapable of transmitting electron beams, and an image formation opticalsystem, all of which are disposed on one optical axis in a manner inwhich a cross-over image to be formed with the electron gun is focusedat a position in the vicinity of a main surface of the objective lenssystem containing a magnetic lens of the image focusing optical system,an image of an aperture for determining an irradiation field is focusedon the sample, the electron beams transmitted through the sample ismagnified with the objective lens to form an magnified image in front ofan magnifying lens disposed at the rear position of the objective lens,and a further magnified image is formed on a detector with themagnifying lens.

In accordance with the present invention 1-3, the electron beam systemis provided which is arranged such that plural beams are formed in thevicinity of one optical axis and then focused to form an image on thesample with the objective lens, the sample surface is scanned with atwo-stage deflector of the objective lens disposed on the side of theelectron gun, secondary electrons generated from a scanning point on thesample are separated from a primary optical system with anelectromagnetic deflector (an E×B separator) after passing through theobjective lens, and the image is formed and detected on the detectorwith an magnifying lens having at least one stage. The electron beamsystem comprises a deflection ratio of the two-stage deflectors isadjusted in such a manner that a deflection pivot of the two-stagedeflectors is located on the side of the electron gun rather than theprincipal plane of the objective lens and further the deflection pivotof the two-stage deflection becomes located between the position atwhich a coma aberration becomes minimal at the time of deflection andthe position at which a deflecting chromatic aberration becomes minimal.

In the present invention 1-4, there is provided the electron beam systemwhich comprises shaping the electron beams emitted from the electron gunwith a shaping aperture, focusing them on a plane of the sample,separating from the primary beam the electrons emitted from the sampleusing the beam separator after passage through the objective lens,magnifying them with plural lenses, and focusing them on the principalplane of the objective lens, wherein the principal light beams of theprimary and secondary beams are arranged so as to pass at differentpositions in a distance between the electrostatic deflector and thesample plane.

The present invention 1-5 provides a defect detection method fordetecting a defect which comprises irradiating a sample with an electronbeam, passing the electron beam through the sample, and detecting anelectron emitted from the sample, reflected from the sample or to bereflected before striking the sample by focusing or focusing on a planeof a detector with an image projecting optical system, the defectdetection method comprising the steps of:

recognizing a region on the sample plane where defect detection iseffected in a die-to-die detection system and a region on the sampleplane where defect detection is effected in a cell-to-cell detectionsystem;

recognizing an x-coordinate of a boundary between the above two regions;

dividing an entire area of a die into stripes each acquiring an image ofthe sample while continually moving a sample stage in a y-direction;

acquiring the image of the sample in a stripe unit and effecting defectdetection; and

dividing the stripe in a manner that an x-coordinate of the stripeexisting at the end is brought in agreement with an x-coordinate of theabove boundaries.

The present invention 1-6 provides the electron beam system wherein theelectron gun, the deflector, the objective lens and the beam separator(an E×B separator) having at least the electromagnetic deflector, thecondenser lens, and the sample are disposed at different positions onthe optical axis, wherein a deflection chromatic aberration generated bythe deflector is offset by a deflection chromatic aberration generatedby the electromagnetic deflector. The electron beam system is furtherconfigured in such a manner that the electron gun, the condenser lensand the deflector are disposed on one optical axis, the objective lensand the electromagnetic deflector are disposed on another optical axisdistant from the optical axis, and the electron beam is deflected withthe deflector toward a central direction of the beam separator having atleast the electromagnetic deflector.

The present invention 1-7 provides the electron beam system wherein theelectron beam emitted from the electron gun is deflected with theelectromagnetic deflector, the electron beam vertically strikes thesample, the secondary particle emitted from the sample is deflected withthe electromagnetic deflector toward a central direction of thedeflector having another optical axis parallel to a normal linedirection of the sample, and the deflected secondary particle iscombined with the other optical axis by means of the deflector.

The present invention 1-8 provides a device production method for theproduction of a device, which comprises the steps of:

preparing a wafer;

carrying out a wafer process; and

evaluating the wafer after the process has been carried out by using theobjective lens according to the present invention 1-1, wherein the abovesteps are repeated as many times as needed to assemble a device.

In order to achieve the objects as described above, the presentinvention 2-1 provides an electron beam system for forming atwo-dimensional image by irradiating a sample with an electron beam andmagnifying an image of a secondary electron emitted from the sample oran image of a transmitting electron transmitting the sample with animage projecting optical system, wherein the sample surface is dividedvirtually into plural stripe regions in a manner that a longitudinaldirection thereof is arranged parallel to a predetermined axis, thestripe region is divided into main field regions, each being rectangularand parallel to a latitudinal direction thereof, the main field isfurther divided into plural subfields, and irradiation with the electronbeams and formation of the two-dimensional image are repeated in a unitof the subfield.

With the configuration of the electron beam system as described above,the electron beams can be irradiated in a unit of small square-shapedsubfields, thereby enabling the increasing of a current density of theelectron beams and improving a transmittance ratio of the secondaryelectrons of the image projecting optical system. Further, the electronoptical mirror mount can be made more compact in size. Moreover, thepresent invention 2-2 permits the formation of the image in a unit ofthe subfields, wherein a correction corresponding to a distance from theoptical axis of each subfield is made whenever the irradiation with theelectron beams or the formation of the two-dimensional image iseffected, and the principal light beams of the secondary electrons orthe transmitting electrons are arranged so as to substantially coincidewith the optical axis of the lens on the downstream side by means of alens of the image projecting optical system for forming thetwo-dimensional image, which is located closer to the sample.

The present invention 2-3 comprises a first-stage lens of the imageprojecting optical system contains a predetermined electromagnetic lens,a deflector having a deflection magnetic field distributionapproximating to a distribution of differential coefficients of an axialmagnetic field distribution of the electromagnetic lens is disposed inthe vicinity of the first-stage lens, and the first-stage lens and thedeflector are operated under a condition approximating to a MOL (movingobject lens) operation condition. Further, the present invention 2-4 iscomprises the first-stage lens of the image projecting optical systemcomprises the electromagnetic lens in which a lens gap to be formed withthe two magnetic poles faces the sample side and an axially symmetricelectrode disposed between the magnetic poles and the sample.

The present invention 2-5 comprises the deflector is enclosed with aninsulating case, the outside face of the insulating member is coatedwith metal, and the metal coated side thereof is applied with voltage.The present invention 2-6 comprises the two-dimensional image by thesecondary electron images is formed on a scintillator plane of a FOP(fiber optical plate) composed of plural optical fibers (cellfock) eachhaving a focusing action.

The present invention 2-7 comprises the scintillator plane is suppliedwith voltage that accelerates electron beams to a better sintilationefficiency. The present invention 2-8 comprises an image is formed whilethe sample placed on a sample stage is being moved continually in oneaxial direction and the position of the sample stage is measured with alaser interferometer and further that a correction is made so as tocause no moving of the two-dimensional image to be focused on thedetector at the time of forming the image of one subfield.

The present invention 2-12 comprises the two-dimensional image to beformed by the secondary electrons is converted into a light image, theconverted light image in turn is condensed to a photoelectric transferdetector acting as a detector through a predetermined optical lens wherethe image is converted into electric signals, and, in the event where apixel size of the two-dimensional image is changed, at least amagnification of the optical lens is varied. The present invention 2-10comprises an electron beam irradiation system for irradiating the samplewith the electron beams is provided with a beam separator having atleast an electromagnetic deflector, the electron beams are generatedfrom a direction at an angle of approximately 2.8α with respect to thenormal line of the sample, and the electron is deflected with theelectromagnetic deflector at an angle of −α with respect to the normalof the sample.

The present invention 2-11 comprises the electron beam irradiationsystem is provided with an aperture in a shape approximating to thesubfield and, in the event where the pixel size of the two-dimensionalimage is to be changed, an aperture with a different dimension isdisposed in vacuum and then aligned on the optical axis.

The present invention 2-12 provides a secondary image-forming method forforming the two-dimensional image by irradiating the sample with theelectron beam and magnifying the secondary electron emitted from thesample or a transmitting electron transmitting the sample with the imageprojecting optical system, the secondary image-forming method comprisingthe steps of; dividing a surface of the sample into plural striperegions in which a longitudinal direction thereof is arranged parallelto a predetermined axis; dividing the stripe region into main fieldregions, each being rectangular and parallel to a latitudinal directionthereof; dividing the main field into plural subfields; repeatingirradiation with the electron beam or formation of the secondary imagein a unit of the subfields; and making a correction of a distance froman optical axis of each subfield whenever the irradiation with theelectron beam and the formation of the secondary image is effected.

As the main field is divided into the subfields and an irradiation areais set to be in a small square-shaped form, a primary beam having a highcurrent density can be irradiated. Further, a combination lens of anelectromagnetic lens having low aberration and an electrostatic lens canbe used as an objective lens. Moreover, as the electron beams having ahigh current density can be used as described above and the imageprojecting optical system has a high transmittance ratio regarding thesecondary electrons, a course of time for irradiation of the electronbeams can be shortened. As a result, an evaluation for samples can beeffected with a high throughput.

The present invention 3-1 provides a pattern evaluation method forevaluating a pattern on a sample by irradiating the sample with pluralelectron beams, which comprises the steps of:

(a) forming multiple beams by using a multi-aperture;

(b) scanning a marker existing on a Z-coordinate on which a sample to beevaluated exists by focusing the multi-beams and using the condensedmultiple beams;

(c) separating the electron beams emitted from a scanning point on themarker from a primary electron beam with a beam separator containing atleast an electromagnetic deflector and detecting the electron beams witha single detector;

(d) evaluating at least one of beam resolution, beam separation and beamintensity by detection with the detector;

(e) leading a secondary electron group emitted from a scanning point onthe sample to a secondary optical system; and

(f) evaluating a pattern on the sample plane by detecting a signalcorresponding to each beam of the multi-beams of the secondary electrongroup with plural detectors.

In the present invention 3-1, there is provided a pattern evaluationmethod for evaluating a pattern on a sample plane by irradiating thesample with plural electron beams, which comprises the steps of:

(a) forming multiple beams;

(b) scanning a sample to be evaluated by focusing the multi-beams andusing the condensed multiple beams;

(c) leading the plural electron beams to a secondary optical system byseparating plural electron beams of a secondary electron group emittedfrom a scanning point on the sample plane by separating the electronbeams from a primary electron beam with an electromagnetic deflector (anE×B separator) and

(d) evaluating a pattern on the sample plane by detecting a signalcorresponding to each beam of the multi-beams with plural detectorscorresponding to the plural electron beams;

wherein a distance between an objective lens of a primary optical systemand a lens disposed upstream thereof is set to be larger than a distancebetween an objective lens of the secondary optical system and a nextlens disposed downstream thereof.

In the pattern evaluation method according to the present invention 3-1,the distance between the objective lens of the primary optical systemand the lens disposed upstream thereof can be set to double or more thandouble the distance between the objective lens of the secondary opticalsystem and the next lens disposed downstream thereof. In the patternevaluation method according to the present invention 3-1, the marker maybe disposed on a flat substrate and may be a dot pattern consisting ofplural dots of heavy metal each having a dimension smaller than the beamdistance or a marker having plural holes each having a dimension smallerthan the beam separation or a pattern in the form of a knife edgemagnifying parallel to the x-axial or y-axial direction and having adimension larger than the beam separation.

Further, the present invention 3-1 provides a device production methodfor the production of a device, which comprises the steps of:

(a) preparing a wafer;

(b) carrying out a wafer process;

(c) evaluating the wafer after the process by means of either of themethods as described above;

(d) repeating the step b and the step c as many times as necessary; and

(e) dividing the wafer into dies and assembling them into a device.

As another embodiment according to the present invention 3-1, there isprovided a pattern evaluation system for evaluating a pattern on asample plane by irradiating the sample with plural electron beams, whichcomprises:

(a) a multiple beam former;

(b) optical system for scanning a sample to be evaluated by focussingthe multiple beams and using the condensed multiple beams;

(c) a beam separator for leading the plural electron beams to asecondary optical system by separating plural electron beams of asecondary electron group emitted from a scanning point on the sampleplane by separating the electron beams from a primary electron beam withan electromagnetic deflector; and

(d) a deflector for evaluating a pattern on the sample plane bydetecting a signal corresponding to each beam of the multi-beams withplural detectors corresponding to the plural electron beams;

wherein a distance between the objective lens of the primary opticalsystem and the lens disposed upstream thereof is set to be larger than adistance between the objective lens of the secondary optical system andthe next lens disposed downstream thereof.

In the above pattern evaluation system, it is advantageous that thedistance between the objective lens of the primary optical system andthe lens disposed upstream thereof be set so as to double or more thandouble the distance between the objective lens of the secondary opticalsystem and the next lens disposed downstream thereof.

As the present invention 3-2, there is provided a pattern evaluationmethod on the sample plane with plural beams, which comprises the stepsof:

(a) forming multiple beams by irradiating plural apertures with anelectron beam emitted from an electron gun having a cathode;

(b) forming a cross-over of a beam passed through the plural apertureson a NA aperture having a dimension substantially larger than adimension of the cross-over or at a position in the vicinity of the NAaperture;

(c) focusing an magnified cross-over at a Z-coordinate position in thevicinity of a principal plane of an objective lens;

(d) forming a reduced image of an image of the multiple beams on thesample plane with at least a reducing lens and an objective lens;

(e) scanning the sample with the multiple beams by using at least atwo-stage deflector disposed between the reducing lens and the objectivelens;

(f) accelerating and focussing a secondary electron group emitted fromthe scanning point on the sample with an objective lens;

(g) deflection the secondary electron group passed through the objectivelens with an electromagnetic deflector and sending it to a secondaryoptical system;

(h) magnifying a mutual separation of the secondary electron group bythe secondary optical system and leading the secondary electron group toplural secondary electron detectors; and

(i) evaluating a pattern on the sample plane from a signal detected withthe detector.

The present invention 3-2 further provides a pattern evaluation methodon the sample plane with plural beams, which comprises the steps of:

(a) forming multiple beams by irradiating plural apertures with anelectron beam emitted from an electron gun having a cathode, which is adiverging beam whose third order spherical aberration is negative orwhich forms no cross-over on the side of the sample other than thecathode;

(b) forming a cross-over of a beam passed through the plural apertureson a NA aperture or at a position in the vicinity of the NA aperture;

(c) focusing an magnified image of the cross-over at a position in thevicinity of a principal plane of an objective lens;

(d) forming a reduced image of an image of the multiple beams on thesample plane with a reducing lens and an objective lens;

(e) scanning the sample with the multiple beams by using at least atwo-stage deflector disposed between the reducing lens and the objectivelens;

(f) accelerating and focussing a secondary electron group emitted fromthe scanning point on the sample with an objective lens;

(g) deflecting the secondary electron group passed through the objectivelens with an electromagnetic deflector (an E×B separator) and sending itto a secondary optical system;

(h) magnifying a mutual separation of the secondary electron group bythe secondary optical system and leading the secondary electron group toplural secondary electron detectors; and

(i) evaluating a pattern on the sample plane from a signal detected withthe detector.

In any one of the above mentioned pattern evaluation methods of thepresent invention 3-2, the lens for forming the cross-over image on theaperture or in the vicinity of the aperture may comprise a condenserlens disposed immediately before or behind the multi-aperture and acondition for exciting the condenser lens may be set as a condition forfocusing an image of the beam passed through an aperture distant fromthe optical axis of the multi-aperture on the aperture.

In any one of the above mentioned pattern evaluation methods of thepresent invention 3-2, all the secondary electron groups emitted fromthe sample plane at an angle within the range of ±90° with respect tothe normal line of the sample plane can be led toward the secondaryelectron detector without being blocked during leading thereof.

As the present invention 3-2, there is provided a device productionmethod for the production of a device, which comprises the steps of:

(a) preparing a wafer;

(b) carrying out a wafer process;

(c) evaluating the wafer after the process by means of either of themethods as described above;

(d) repeating the step b and the step c as many times as necessary; and

(e) dividing the wafer into dies and assembling them into a device.

The present invention 3-3 provides a pattern evaluation method forevaluating a pattern by scanning the pattern on a sample with pluralelectron beams, which comprises the steps of:

(a) forming multiple beams;

(b) reducing the plural beams and focusing them on a plane of the samplewith at least a two-stage lens;

(c) concurrently scanning the plane of the sample by the plural beamswith a deflector;

(d) accelerating and focussing a secondary electron emitted from ascanning point on the sample, a reflected electron or a transmittingelectron toward a direction of an objective lens and transmitting itthrough the objective lens;

(e) separating the plural secondary electron beams passed through theobjective lens from a primary optical system with an electromagneticdeflector (an E×B separator) and

(f) magnifying a mutual separation of the plural secondary electronbeams with a secondary optical system and sending to a detector;

wherein an outer shape of a lens disposed immediately behind theelectromagnetic deflector is in the form of a cone or a truncated conehaving a vertex with a small radius.

In the present invention 3-3, there is also provided a patternevaluation method for evaluating the pattern by scanning the pattern onthe sample with plural electron beams, which comprises the steps of:

(a) generating plural beams;

(b) reducing the plural beams and focusing them on a plane of the sampleby using at least a two-stage lens;

(c) concurrently scanning the plane of the sample by the plural beamswith a deflector;

(d) accelerating and focussing a secondary electron emitted from ascanning point on the sample, a reflected electron or a transmittingelectron toward a direction of an objective lens and transmitting itthrough the objective lens;

(e) magnifying plural secondary electron beams passed through theobjective lens with an image-forming optical system; and

(f) detecting plural secondary electron beams magnified by theimage-forming optical system with a detector corresponding to a numberof the secondary electron beams and forming a two-dimensional image,

wherein a one-stage lens of at least the two-stage lens has threeelectrodes in which a central electrode comprises an electrostatic lensor an electromagnetic lens to which a positive high voltage is applied.

In the pattern evaluation method according to each of the presentinventions 3-3, it is advantageous that a system for generating theplural beams comprises a system in which the plural apertures areirradiated with electron beams emitted from the electron gun having acathode with its sharp tip. Further, in the pattern evaluation methodsaccording to the first and second modes of the present invention 3-3, itis advantageous to use a system having plural optical axes forgenerating the plural beams.

In the present invention 3-3, there is further provided a deviceproduction method for the production of a device, which comprises thesteps of:

(a) preparing a wafer;

(b) carrying out a wafer process;

(c) conducting an evaluation of the wafer after the process by usingeither of the methods described above;

(d) repeating the step b and the step c as many times as necessary; and

(e) dividing the wafer into dies and assembling them into a device.

As another mode according to the present invention 3-3, there isprovided a pattern evaluation system for evaluating a pattern on theplane of a sample by scanning the pattern on the plane of the samplewith plural electron beams, which comprises:

(a) a multiple beam generator;

(b) lens system for the plural beams and focusing them on a plane of thesample with at least a two-stage lens;

(c) a deflector for concurrently scanning the plane of the sample by theplural beams with a deflector;

(d) an objective lens for accelerating and focussing a secondaryelectron emitted from a scanning point on the sample, a reflectedelectron or a transmitting electron;

(e) a lens separater for separating plural secondary electron beamspassed through the objective lens from a primary optical system with anelectromagnetic deflector and sending it to a secondary optical system;and

(f) an optical system for magnifying a mutual interval between theplural secondary electron beams with a secondary optical system andsending it thereto;

wherein an outer shape of a lens disposed immediately before theelectromagnetic deflector is of a conical shape or of a truncatedconical shape with a convex having a small radius.

In the pattern evaluation system according to the present invention 3-3,it is advantageous that a system for generating the plural beamscomprises a system in which the plural apertures are irradiated withelectron beams emitted from the electron gun having a cathode with itssharp tip. Further, in the pattern evaluation methods according to thepresent invention 3-3, it is advantageous to use a system having pluraloptical axes in the step for generating the plural beams.

The present invention 4-1 provides a pattern-delineating method forforming a pattern by an exposure of electron beams to a wafer coatedwith a resist, which comprises the steps of:

(a) accelerating an electron beam emitted from a cathode discharging athermo electron and sending it to a square-shaped aperture to shape theelectron beam into a square-shaped form;

(b) forming a pattern of the electron beamshaped in a square-shaped formby passage through a character mask and sending the patterned electronbeam; and

(c) reducing the patterned electron beam, aligning it, focusing it withan objective lens and irradiating the wafer therewith;

wherein the patterned electron beam is accelerated between the objectivelens and the wafer into energy to transmit through the resist.

In the pattern-delineating method as described firstly in the presentinvention 4-1, the cathode can be operated under space-charge limitconditions. In the pattern-delineating method as described firstly inthe present invention 4-1, it is advantageous that the energy of theelectron beam is set within a range from 1 to 5 keV upon striking thesquare-shaped aperture and sending after being patterned. In thepattern-delineating method as described firstly in the present invention4-1, it is advantageous that the objective lens and the main deflectorare of an electromagnetic type and the other lenses and the deflectorare of an electrostatic type.

In the present invention 4-1, there is provided a device productionmethod for producing a device which comprises the steps of:

(a) preparing a wafer;

(b) carrying out a wafer process;

(c) effecting an evaluation of the wafer after the process by means ofeither of the methods as described above;

(d) repeating the step b and the step c as many times as necessary; and

(e) dividing the wafer into dies and assembling them into a device.

The present invention 4-2 provides a pattern-delineating method forforming a pattern with electron beams, which comprises the steps of:

(a) determining a pattern-delineating layer on which the pattern is tobe formed with an electron beam;

(b) dividing a chip region into plural stripes each having a small widthequal to or smaller than a dimension of a main field of an electronoptical system for the pattern-delineating layer to which the pattern isto be formed with the electron beam;

(c) extracting a pattern which is divided by a boundary line of thestripes in the pattern-delineating layer;

(d) extracting a pattern of problem, among the patterns to be divided,which may cause a problem if divided;

(e) reviewing whether a number of the patterns of problem of problem isreduced by setting a stripe width to a small dimension within apredetermined scope and determining the stripe width to the smalldimension for the reduced number of the patterns of problem in all thepattern-delineating layers, if a number of the patterns of problem wouldbe reduced more than preset when reviewed above; and

(f) forming a pattern by a variable stripe so as for a dimension of amain field to meet the stripe width having the smaller dimensiondetermined by using an electron beam.

The present invention 4-2 further provides a pattern-delineating methodfor forming a pattern by an electron beam, which comprises the steps of:

(a) determining a layer to which a pattern is formed by the electronbeam;

(b) dividing a chip region into plural stripes each having a small widthequal to or smaller than a size of a main field of an electron opticalsystem for the pattern-delineating layer to which the pattern is to beformed with the electron beam;

(c) extracting a pattern which is divided by a boundary line of thestripes in the pattern-delineating layer;

(d) extracting a pattern of problem, among the patterns to be divided,which may cause a problem if divided;

(e) reviewing whether the pattern of problem does not exist any longerby making the boundary line of the stripes in an uneven shape;

(f) reviewing whether, in the event where a dimension of a substantiallyeffective main field of an electron optical system is expressed as L, adimension between a convex portion of an uneven shape of a stripe havinga boundary line of the uneven shape and another convex portion thereofexceeds the dimension L;

(g) bringing a direction of unevenness of the uneven shape of theboundary line of the stripes reviewed in the step e in at least twolayers into agreement with each other for all the layers to which thepattern is to be formed with the electron beams, on condition that adifference of an x-coordinate and a y-coordinate between the boundaryline of the stripes in each layer is equal to or smaller than a presetvalue between at least two layers, when it is reviewed in step (f) andprovided that the dimension between the two convex portions does notexceed the dimension L;

(h) reviewing whether a new pattern of problem which is divided by theboundary line does not exist as a result of step (g) and determining anuneven shape of the boundary line of the stripes when such a new patternof problem does not exist as a result of reviewing in step (g); and

(i) forming a pattern by delineating with electron beams in accordancewith the stripes having the uneven shapes determined in step (h).

In the present invention 4-2, there is further provided apattern-delineating method for delineating a pattern with electronbeams, which comprises the steps of:

(a) dividing a layer into plural stripes on which a pattern is to beformed with electron beams;

(b) extracting a pattern to be divided by a boundary line of stripes;

(c) extracting a pattern of problem from the patterns to be dividedthereby, which may cause a question if divided;

(d) reviewing whether a number of the patterns of problem is reduced bysetting a stripe width to a small dimension within a predetermined scopeand, in the event where the review reveals that the number of thepatterns of problem is reduced more than preset, and setting all thestripe widths to the small dimension for the patterns of problem whichmay cause a problem with a precision of alignment among plural layersfor forming a pattern with electron beams; and

(e) providing two mutually neighboring stripes with an overlap region,the mutually neighboring stripes having a boundary line in common whichdivides the pattern of problem, in the event where the pattern ofproblem to be divided by the boundary line thereof still remains as aresult of reviewing in step (d), and carrying out a double exposure tolight for the pattern of problem in the overlap region in such a mannerthat, for each stripe, an amount of exposure to light for the dividedpattern of problem is reduced stepwise from its central portion to itsend and a total amount of exposure to light for the divided pattern ofproblem is equal to that of another pattern.

In a pattern-delineating method described firstly, secondly or thirdlyin the present invention 4-2, it is advantageous that the pattern isformed with the electron beam system in which the LaB₆ cathode isoperated under space-charge limit conditions, the landing energy for thewafer is set to 3 KeV or lower, a cell portion of the pattern is formedby a character projection system while the other portion of the patternis formed by a variable sharpening system, and a distance between acharacter mask and the wafer is set to 30 cm or smaller.

The present invention 4-2 further provides a device production methodfor the production of a device, which comprises the steps of:

(a) preparing a wafer;

(b) carrying out a wafer process;

(c) evaluating the wafer after the process by means of either of thepattern evaluation methods as described above;

(d) repeating steps (b) and (c) as many times as necessary; and

(e) dividing the wafer into dies and assembling them into a device;

in which a lithography process among the steps for carrying out thewafer process is carried out by the above pattern-delineating method.

In the present invention 4-3, there is provided a mask repair method forscanning the finely narrowed mask with electron beams, filling a portionin the vicinity of the optical axis of the mask with reactive gas, andselectively etching a mask or depositing, which comprises the steps of:

(a) obtaining an image of a region containing a location of a defect ona plane of the mask with a scanning electron microscope, that is, a SEMimage;

(b) identifying the location of the defect and determining a regionwhich is to be scanned by electron beams;

(c) scanning the region determined by step (b) with electron beams byfilling the area in the vicinity of the optical axis of the mask withreactive gas;

(d) obtaining a two-dimensional image by scanning a region containingthe location of the defect with electron beams, wider than the areascanned in step (c); and

(e) deciding a completion of repairing on the basis of the imageobtained by step (d).

In the repair method as described firstly in the present invention 4-3,a secondary electronic signal can be used at the time of obtaining theSEM image, the secondary electronic signal being obtained by absorbingelectrons in an electrode which are generated as a result of secondaryelectron multiplication that is caused to occur upon collision of thesecondary electrons with gases. In the repair method as describedfirstly in the present invention 4-3, it is advantageous to use a signalused for the detection of the secondary electrons, when the SEM image isto be obtained, which are accelerated and condensed in an electric fieldformed on the mask and the pressure control aperture, passed throughthem, and deflected toward the secondary electron detector with an E×Bseparator. In the repair method as described firstly in the presentinvention 4-3, the pressure and kind of the gas on the mask can bechanged at the time of repairing and obtaining the SEM image. Further,the present invention 4-3 can provide a device production method for theproduction of a device characterized in that lithography is carried outby using the mask which is repaired by either of the methods asdescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in section showing an objective lens composed of acombination of an electromagnetic deflector and an electrostaticdeflector according to an embodiment of the present invention 1-1.

FIG. 2 is a schematic representation showing a defect inspection systemfor a stencil mask according to an embodiment of the present invention1-2.

FIG. 2B is a view showing a relationship of a distribution of an axialmagnetic field with the trajectory of a beam in a magnetic lens.

FIG. 2C is a view for explaining a velocity vector of a beam on avirtual plane of FIG. 2.

FIG. 3 is a schematic representation showing an electron optical systemfor multiple beams according to an embodiment of the present invention1-3.

FIG. 3B is a representation showing a relationship of a deflection pivotand an aberration in the electron optical system of FIG. 3.

FIG. 4 is a schematic representation showing an electron optical systemwith its detecting plane reduced to a smaller dimension to obtain a highresolution by scanning with large beams according to an embodiment ofthe present invention 1-4.

FIG. 5 is a schematic representation showing an optical system forremoving a deflection chromatic aberration of a beam separator accordingto an embodiment of the present invention 1-6.

FIG. 6 is a schematic representation showing a stripe-dividing processin the defect inspection method according to an embodiment of thepresent invention 1-5.

FIG. 7 is a flowchart showing a process for the production of asemiconductor device according to the present invention 1-8.

FIG. 8 is a flowchart showing a lithography process of the semiconductordevice production method of FIG. 7.

FIG. 9 is a schematic block diagram showing the electron beam systemaccording to an embodiment of the present invention 2-1.

FIG. 10 is a view showing a state of a division of a sample surface intoa stripe region, a main field region and a subfield region.

FIG. 11 is an magnified view in section showing an objective lensaccording to an embodiment of the present invention 2-3.

FIG. 12 is a graph showing a distribution of axial magnetic fieldintensities in the vicinity of a sample and their differentialcoefficients.

FIG. 13 is a schematic block diagram showing an electron beam systemaccording to an embodiment of the present invention 2-10.

FIG. 14 is a schematic representation showing an electron optical systemto be used in an embodiment of the present invention 3-1.

FIG. 15 is a plane view showing various dots to be used for a pattern ofa marker.

FIG. 16 is a schematic representation showing a configuration of aFaraday cup to be used as a single secondary electron detector.

FIG. 17 is a diagram for explaining a beam resolution.

FIG. 17 b is a schematic plan view of a Farady cup and a knife edge formeasuring a beam solving power.

FIG. 17 c is a schematic elevational section of the Farady cup shown inFIG. 17 b.

FIG. 18 is a schematic representation showing an electron optical systemto be used in an embodiment of the present invention 3-2.

FIG. 19 is a schematic representation showing an electron optical systemto be used in an embodiment of the present invention 3-3.

FIG. 20 is a view showing arrangements for multiple beams to be used inan embodiment of the present invention 3-3.

FIG. 21 is a schematic representation showing a pattern-drawing systemto be used for the pattern-delineating method in an embodiment ofpresent invention 4-1.

FIG. 22 is a schematic representation showing an electron beam system tobe used in the present invention 4-2.

FIG. 23 is an magnified view showing three layers at locations in thevicinity of upper left side in the first embodiment of the presentinvention 4-2.

FIG. 24 is an magnified view showing a location in the vicinity of theboundary line of the stripes in the second embodiment of the presentinvention 4-2.

FIG. 25 is an magnified view showing a location in the vicinity of theboundary line of the stripes in the third embodiment of the presentinvention 4-2.

FIG. 26 is a schematic representation showing a mask repair system to beused for the first mode according to the present invention 4-3.

FIG. 27 is a schematic representation showing a mask repair system to beused for the second mode according to the present invention 4-3.

EXPLANATION OF REFERENCE NUMERALS AND SIGNS

-   -   100: objective lens system,    -   101: optical axis,    -   103: inner magnetic pole,    -   105: outer magnetic pole,    -   105 a: plane of outer magnetic pole forming magnetic gap,    -   105 b: inside plane of outer magnetic pole plane forming        magnetic gap,    -   109: exciting coil,    -   117: electrostatic deflector,    -   119: electromagnetic deflector for beam separator,    -   121: trajectory of secondary beam,    -   123: obtuse-angled cross section,    -   125: additional member for getting rid of an acute-angled        portion of a magnetic material,    -   127: axially symmetric electrode,    -   129: hermetic sealing,    -   131: vacuum sealing member,    -   133: O-ring,    -   201: electron gun,    -   205: shaping aperture,    -   207: irradiating lens,    -   211: objective lens,    -   219: magnifying lens,    -   223: first magnified image,    -   225: FOP window coated with scintillator,    -   303: condenser lens,    -   309: multi-aperture,    -   305: rotating lens,    -   307: NA aperture,    -   311: reducing lens,    -   313: objective lens,    -   317: axially symmetric electrode,    -   323: beam separator having an electromagnetic deflector,    -   325: scanning deflector.    -   327: direction of deflection of beam separator at sample plane,    -   329: direction of deflection of beam separator,    -   331: direction of secondary optical system,    -   333: rotation of secondary electrons with objective lens,    -   335: fulcrum of scanning deflection,    -   337: second magnifying lens,    -   339: lens gap,    -   341: magnetic shield for minimizing leakage of magnetic field,    -   343: third magnifying lens,    -   345: scintillator plane,    -   347: optical lens,    -   349: PMT arbeam,    -   351: aperture for adjusting signal intensity,    -   353: deflector for dynamic correction,    -   355: exciting coil,    -   359: O-ring,    -   357: vacuum sealing ring,    -   401: electron gun,    -   403: multi-aperture,    -   405: condenser lens,    -   407: objective lens,    -   411: cross-over,    -   413: beam separator having an electromagnetic deflector,    -   415: trajectory of principal light beams of primary beams,    -   417: cross-over image,    -   419: scanning deflector,    -   423: image of secondary beams,    -   427: MCP,    -   429: deflector for dynamic correction.    -   431: light magnifying lens,    -   433: PMT array,    -   501: electron gun,    -   503: condenser lens,    -   505: axis-aligning deflector,    -   507: trajectory of principal light beams of primary beams,    -   511: electrostatic deflector for beam separator,    -   513: electromagnetic deflector for beam separator,    -   515: objective lens,    -   519: amount of deflection with electromagnetic deflector,    -   521: amount of deflection with electrostatic deflector,    -   523: trajectory of secondary beams,    -   601: die,    -   603: region for dye-to-dye inspection,    -   605: cell-to-cell inspectable region,    -   607: stripe width of stripe containing cell-to-cell inspectable        region,    -   609: stripe for die-to-die inspection region, S: sample.    -   A: electron beam system,    -   A₁: primary optical system (electron beam irradiation optical        system)    -   a₂: secondary optical system (image projection optical system)    -   a₃: stage part,    -   1: electron gun,    -   2: condenser lens,    -   3: square-shaped aperture,    -   4: point of formation of cross-over,    -   5: condenser lens,    -   6: deflector,    -   7,    -   8: beam separator having an electromagnetic deflector,    -   9: electrostatic deflector,    -   10: objective lens,    -   11: electromagnetic deflector for MOL operations,    -   12: stage, S: sample,    -   14: laser-moving mirror,    -   15: laser-stationary mirror,    -   16: reflecting mirror,    -   17: beam separator,    -   18: beam receiver and oscillator,    -   19: second magnifying lens,    -   20: NA aperture,    -   21: point of cross-over formation.    -   22: FOP,    -   22 a: scintillator plane,    -   23: zoom-magnifying optical lens,    -   24: detector (CCD camera),    -   26: stripe region,    -   27: subfield,    -   28: trajectory for MOL,    -   29: small aperture,    -   30: power source,    -   31: inner magnetic pole,    -   32: outer magnetic pole,    -   34: vacuum sealing tube,    -   35: O-ring,    -   36: hermetic sealing,    -   37: electromagnetically deflection coil 1 for MOL,    -   38: electromagnetically deflection coil 2 for MOL,    -   39: ceramic case,    -   91: point of formation of first image,    -   92: normal line of sample plane,    -   93: trajectory for avoidance of a space-charge effect, W: stripe        width.    -   701, 801, 901: cathode,    -   702, 802, 902: Wehnelt,    -   703, 803, 903: anode,    -   705, 706, 804, 805, 808, 809, 904, 905: axis-aligning deflector,    -   707, 806, 906, 907, 909: condenser lens,    -   708, 807, 910: multi-aperture,    -   709, 710: deflector for aligning axis of NA aperture with axis        of reducing lens,    -   711, 810, 913: NA aperture,    -   712, 811, 914, 915, 917: reducing lens,    -   713, 812: scanning deflector,    -   715, 716, 814: beam separator,    -   717, 815, 921, 922, 924: objective lens,    -   719, 721, 818, 820, 928, 929, 930: magnifying lens,    -   720, 722, 819, 821, 931, 935: axis-aligning deflector,    -   723, 822, 936: MCP,    -   726: Faraday cup,    -   727, 728, 729, 730: dot,    -   740, 823: multi-anode,    -   741, 824, 937: resistance,    -   742, 825: multi-amplifier,    -   743, 825, 938: A/D converter,    -   744, 826, 939: image forming circuit,    -   827, 940: comparator,    -   828: tungsten filament for heating,    -   829: axially symmetric electrode.    -   451: LaB₆ cathode,    -   452: Wehnelt,    -   453: anode,    -   454: beam shaping aperture,    -   455: shaping lens (condenser lens),    -   456: shaping lens,    -   457: shaping deflector,    -   458: blanking deflector,    -   459: character mask,    -   460: NA aperture,    -   461: reducing lens,    -   462: objective lens,    -   463, 464, 465, 466: main deflector,    -   467: laser oscillator and light receiver,    -   468: reflecting mirror,    -   469: beam splitter,    -   470: laser-stationary mirror,    -   471: laser-moving mirror,    -   472: electrostatic chuck,    -   473: electrostatic chuck electrode,    -   474: y-stage,    -   475: x-stage,    -   476: high-voltage power source (positive power source),    -   477: wafer;    -   478: electrostatic deflector;    -   479: electrostatic deflector;    -   480: power source (chuck power source),    -   551: cathode,    -   552: Wehnelt,    -   553: anode,    -   554: square-shaped aperture,    -   555: lens,    -   556: electrostatic deflector,    -   557: character selecting deflector,    -   558: lens,    -   559: character mask,    -   560: correcting deflector,    -   561: NA aperture,    -   562: reducing lens,    -   563: objective lens,    -   564: electromagnetic deflector.    -   565: wafer,    -   566: blanking deflector,    -   567: sub-field deflector,    -   571: divided stripe of gate layer,    -   572: divided stripe of first contact hole layer,    -   573: divided stripe of second contact hole layer,    -   574, 575, 576, 577: stripe boundary line,    -   581: stripe boundary line to be determined from substantially        maximum field of EO,    -   582: stripe boundary line at layer forming source, drain        pattern,    -   583: pattern,    -   584: stripe boundary line at gate layer,    -   585: pattern at gate layer,    -   586: stripe boundary line at contact hole layer,    -   587: contact hole pattern,    -   141: stripe boundary line to be determined from substantially        maximal field of EO,    -   142: stripe boundary line having a small crossing with pattern        by making stripe width smaller,    -   143: pattern,    -   144: pattern,    -   145: pattern crossing boundary line,    -   146: left stripe,    -   156: right stripe,    -   147 or 155: smaller-divided pattern,    -   162: overlap region (substantially maximal field of EO=maximal        field of EO minus field to be used for correction)    -   651: electron gun cathode,    -   652: Schottkey shield,    -   653: anode,    -   654: condenser lens,    -   655: reducing lens,    -   656: objective lens,    -   657: pressure-limiting aperture and NA aperture,    -   658: lens gap,    -   659: mask,    -   660: gas inlet,    -   661: rotary pump,    -   662: mechanical booster,    -   663, 664: TMP pump,    -   665: scanning deflector,    -   666: scanning power source,    -   667: CRT monitor,    -   668: resistance,    -   669: amplifier,    -   670: pattern image,    -   671: black defect,    -   672: scan upon correction of defect,    -   673: guard ring for differential exhaust,    -   674: XY-alignment mechanism,    -   675: white defect,    -   676: scanning region upon correction of white defect,    -   681: positive power source,    -   682: sealing member,    -   688: O-ring,    -   684: electrostatic deflector for beam separator,    -   685: electromagnetic deflector for beam separator,    -   686: insulating spacer,    -   687: trajectory of secondary electron,    -   688: detector for secondary electrons.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

FIG. 1 shows a cross-sectional shape of an objective lens system 100 tobe used for an electron beam system in accordance with the presentinvention 1-1. An actual structure of the objective lens system 100 canbe represented by rotating it around the optical axis 101. An electrongun is disposed at an upper side of FIG. 1, although not shown herein,and primary electron beams generated from the electron gun are focusedonto the surface of a sample S through the optical axis with theobjective lens system 100. The objective lens system has a structuresurrounding the exciting coil 109 with the inner magnetic pole 103disposed on the side of the optical axis, the outer magnetic pole 105disposed on the side opposite thereto, and the magnetic circuit 107, andit is arranged such that the lens gap 111 is located having an aperturedirected toward sample S. Reference numeral 115 refers to a beamseparator for deflecting secondary electrons to be emitted from thesample toward sample S and may comprise the electrostatic deflector 117and the electromagnetic deflector 119. Reference numeral 121 refers toan trajectory of the principal light beams of the secondary electrons. Anegative high voltage is applied to sample S.

The objective lens system 100 to be used for the present invention maybe arranged, unlike the conventional objective lens systems, in such amanner that the lens gap may have a truncated-conical shape in crosssection in which the optical axis thereof is not parallel to the opticalaxis and the radius on the side of the sample becomes smaller and thaton the side of the electron gun becomes larger. A simulation hasrevealed that the lens gap in the shape of the truncated cone can reducea number of the ampere turns (ATs) of the exciting current for obtainingfocusing conditions by approximately a half as compared to when the lensgap is disposed in parallel to the optical axis.

The inner magnetic pole 103 is disposed as part of a conical structurehaving an angle greater by more than 45° with respect to the opticalaxis in order to permit the mounting of the beam separator 115.Similarly, the outer magnetic pole 105 constitutes a part of an innerside of the conical structure. By setting the angle of the conicalplanes of the inner magnetic pole 103 and the outer magnetic pole 105with respect to the optical axis 101 to 45° or greater, a materialhaving a magnetic pole with small magnetic flux density and a lowersaturated flux density can be used. Such a structure of the magneticpole, however, may cause the problems of a magnetic flux density passingthrough each of the magnetic poles is rendered larger at a portion atwhich the inner magnetic pole 103 faces the outer magnetic pole 105,thereby resulting in approximation to the saturated flux density

In particular, in the event where the inner surface of the outermagnetic pole 105 is configured in such a conical shape, a portionhaving an acute-angled cross section at the portion of the obtuse-angledcross section 123 is formed on the side of the sample of the lens gap.If this state would be sustained as it is, the magnetic flux isconcentrated onto the acute-angled portion resulting in too large amagnetic flux density and a saturation of permeability rate of aferromagnetic material. If the permeability rate would be saturated, themagnetic flux will not pass through the original position resulting inexpanding magnetic density on the axis in the axial direction andworsening aberration characteristics. In order to avoid this occurrence,an additional member 125 can be added to make the angle at the portion123 an obtuse angle and to change no inner conical shape as well. Bychanging the angle of the cross-sections of the inner and outer magneticpoles in the vicinity of the sample to an angle of 90° or greater, theproblem with a saturation of the magnetic permeability ratio of themagnetic material can be avoided.

The exciting coil 109 is actually arranged such that the outer diameteris further made larger so as to enlarge the Z-directional dimension,thereby permitting a large number of large wires to be wound thereon.Reference numeral 127 is an electrode of an axially symmetric disc typeto which a positive high voltage is applied in order to make thepotential larger at a position where the axial magnetic field is large.This electrode is fixed to the outer magnetic pole 105 through aninsulating spacer (not shown). In order to improve concentricity betweenan aperture of the inner magnetic pole 103 and a pole of the mainelectrode, the hole of the electrode 127 may be subjected to finalsharpening after the lenses have been assembled as a whole, followed bydissembling, washing and re-assembling. A lead wire for applying highvoltage to the electrode 127 may be disposed leading outside by mountingthe hermetic seal 129 between both of the magnetic poles or leading fromthe lower portion of the outer magnetic pole 105. Reference numeral 131refers to a vacuum wall member for separating the exciting coil portion109 from the vacuum part of the electron beam system in order to permitthe exciting coil portion 109 to be disposed in the atmosphere, and thevacuum sealing member 131 is kept in a vacuum state with the O-ring 133.

Alignment of the core of the electromagnetic deflector 119 of the beamseparator 115 in common with the inner magnetic pole 103 can achieve animproved concentricity of the objective lens system 100 with eachdeflector of the beam separator 115. Reference numeral 117 refers to anelectrostatic deflector of the beam separator 115, which is of anintegral structure made of ceramic so as for the outer size to assume asmall dimension. In the embodiment as depicted in the drawing, theconical planes 105 a and 105 b of the outer magnetic pole are eacharranged so as to assume a different angle with the optical axis. Thisfeature has been found appropriate by a simulation, however, it is to benoted that they may be on an equal conical plane.

As described above, the embodiment as illustrated in FIG. 1 can providean objective lens system that can reduce the number of the ampere turns(ATs) of the exciting current for obtaining focusing conditions and thatcan avoid the problem with the saturation of the magnetic permeabilityof the magnetic material.

Second Embodiment

FIG. 2 shows an optical system of an inspection apparatus for atransmission mask using the objective lens system according to thepresent invention. The optical system of the inspection apparatus may bedisposed in such a manner that the LaB₆ cathode electron gun 201 isoperated under space-charge limit conditions, electrons generated fromthe electron gun 201 are condensed with the condenser lens 203, theshaping rectangular aperture 205 are irradiated with the electron beamsat a homogeneous intensity, and an image is formed on a stencil mask(sample) 209 with the irradiating lens 207. Then, a cross-over imageformed with the electron gun is formed on a principal plane of theobjective lens 211. The objective lens 211 is set to have a still largeraxial magnetic field at the position of the sample S. Therefore, theelectrons emitted in the normal direction from the sample S do not crossthe optical axis at a cross-over 213.

Hitherto, the principal light beams from the irradiating lens 207 aresent vertically to the stencil mask 209. With this structure, the beamscoming vertically from the stencil mask 209 disposed at the positionwhere the axial magnetic field is not zero do not intersect with theoptical axis at the cross-over 213. Therefore, the conventional systemis provided with a NA aperture at this position so that it presents theproblem that an image at the peripheral portion may become darkenedbecause the beams coming from the positions distant from the opticalaxis are blocked by the NA aperture to an extent greater than needed.

In the present invention 1-2, the principal light beams from theirradiating lens 207 are sent at an angle crossing the principal planeof the objective lens 211 in such a manner as represented by referencenumeral 215, unlike the above conventional system where they are sentvertically to the sample S. Therefore, the cross-over image can beformed at 213 so that the NA aperture can be disposed at this position,thereby resulting in a decrease of aberration.

This embodiment according to the invention 1-2 will be described in moredetail. In this embodiment, the electron beams are condensed with themagnetic lens while rotating them around the optical axis. Therefore, asshown in FIG. 2B, as the sample is located at the position where theaxial focal distribution is zero, the beams generated vertically fromthe position, e.g., the beams generated from the points A and B of thesample, are rotated toward the points A′ and B′, respectively, on avirtual plane as indicated by dotted lines, as shown in FIG. 2C.Therefore, the trajetories are not parallel to the axis Z (the opticalaxis) at the points A′ and B′ and they have a component of therotational direction as indicated by a “velocity vector”. Only the beamshaving the trajetories as indicated above can form a cross-over at thepoint C, i.e., crosses the optical axis. If the sample is located at theposition on a virtual plane, the beams emitted vertically therefrom donot intersect with the optical axis at the point C because they do nothave any velocity vector in the rotational direction. If the beamsoutgoing from the points A and B would have a radiation component only,but no vertical component, they form a cross-over when they are focusedat the position where the axial magnetic field of the lens is zero.Generally, the beams which have formed a cross-over at the positionwhere the axial magnetic field is zero form a cross-over when they arefocused at the position where the axial magnetic field of the lens iszero.

In the embodiment as shown in the drawing, the principal light beams ofelectron beams outgoing from the stencil mask 209 are beams which focusin the radial direction, but which have an angle in the directionallyangled direction with respect to the normal lines. Therefore, the beamsare directed toward the principal plane of the objective lens 211 whilerotating, and they form a cross-over and at the same time intersect withthe optical axis. The beams cross the optical axis at the cross-over 213formed with the magnifying lens 219, accordingly, so that the NAaperture 217 can be disposed at the position 213 forming an image of ahigh resolution.

Reference numeral 215 refers to an image-forming line of the cross-over.The stencil mask S is fixed to a stage, and an investigation is carriedout while a sample stage 221 is continually moved in the latitudinaldirection of a rectangle-shaped irradiation region. Transmittingelectrons emitted from the stencil mask S form an magnified image withthe first magnifying lens 223, which in turn is further magnified withthe magnifying lens 219 forming an image at the FOP (fiber optics plate)window 225 with a scintillator coated thereon. The image is thenconverted to a light image on the scintillator plane, and the lightimage is withdrawn outside vacuum with the FOP window and detected withthe optical lens on the detection plane of TDI or CCD detector, followedby conversion into electrical signals and formation of an image toeffect the detection of a defect.

Third Embodiment

FIG. 3 shows an embodiment in which the objective lens according to thepresent invention 1-3 is used for an optical system for irradiation withmulti-beams. The electron gun 301 is arranged such that a LaB₆ cathodeelectron gun is operated under space-charge limit conditions insubstantially the same manner as described in the embodiment as shown inFIG. 2. The electron beams emitted from the electron gun 301 form across-over at the NA aperture 307 in an association of the condenserlens 303 with the rotating lens 305 whose rotation can be adjusted.Multiple beams are formed by mounting the multi-aperture 309 in front ofthe rotating lens 305. The condenser lens 303 adjusts a density of beamcurrent at the multi-aperture by varying a cross-over magnification atthe NA aperture 307 without forming a cross-over in association with thelens 305 disposed adjacent thereto. In the optical system, all thelenses are needed to align the posture of the multiple beams with theordinates on the sample because they are all electromagnetic lenses.

The rotating lens 305 has two lens gaps which are set so as to have themagnetic fields at the lens gaps in the opposite directions, therebyenabling the adjustment of an amount of rotation without changing lensintensity by the magnetic fields generated at both lens gaps. The beamsshaped with the multiple beams into the multi-aperture 309 are reducedwith the reducing lens 311 and the objective lens 313, thereby focusingthe multiple beams onto the sample S in a finely narrow form. Theaberration and the beam current value can be optimized by optimizing thedimension of the NA aperture 307 at this timing. The objective lens 313has the magnetic pole on the side of the sample S and the perforatedelectrode 317 of an axially symmetric type for applying the positivehigh voltage is disposed between the objective lens 313 and the sampleS, thereby reducing an aberration constant

The beam separator 323 containing the electrostatic deflector 319 andthe electromagnetic deflector 321 is disposed inside the objective lens313. The secondary electrons emitted from the sample S are acceleratedand condensed with the objective lens 313 and deflected with the beamseparator 323 to the right, when the drawing is viewed, leading to thesecondary optical system. A simulation reveals that the primaryelectrons are rotated by approximately 103° with the objective lens 313and the secondary electrons are rotated by approximately 115° in theopposite direction.

The beam separator 323 is applied with direct voltage and direct currentfor deflection while voltage and current having constant values areapplied always regardless of scanning. On the other hand, a sawtoothwave is applied for scanning and alternating voltage is applied to theelectrostatic deflector 325 and the electromagnetic deflector 319 of thebeam separator 323. Therefore, the electrostatic deflector 319 of thebeam separator 323 is fed with the direct voltage for operations ofseparating the secondary electrons and with the amtooth wave forscanning the primary electron in a superimposed way.

The beam separator 323 causes no deflection primary beams but produces adeflection chromatic aberration. In other words, the beam separatorpermits the primary beams having a constant beam energy to pass straightbut slightly deflects the electron beams having energy somewhatdifferent therefrom without passing straight, i.e., produces a chromaticaberration. In the event where the direction of the deflectionaberration produced by the beam separator 323 and the direction of thedeflection aberration produced by the electrostatic deflector 325 arechanged by 90°, the deflection aberrations of the two deflectors are notadded to each other. For an apparatus for inspecting the sample stagewhile continuously moving it in a y-direction, the deflection directionof the beam separator 323 may be preferably set to rotate in ay-direction on the sample plane because the scanning direction is largerin an x-direction than in the y-direction.

Therefore, the direction of the secondary optical system may bepreferably arranged in such a manner that the objective lens is rotatedby 115° with respect to the y-direction after passage through theobjective lens 313. This feature is indicated in FIG. 3( b). In thisfigure, reference numeral 327 refers to a scanning direction on thesample by the sawtooth wave of the electrostatic deflector 325 and theelectrostatic deflector 319 of the beam separator, reference numeral 329to the deflection direction of the beam separator on the sample by thedirect voltage of the electrostatic deflector 319 and the voltage of theelectromagnetic deflector 321, reference numeral 331 to a direction ofthe secondary optical system, and reference numeral 333 to a rotation ofthe secondary electrons caused by the objective lens 313.

The trajectory of the principal light beams at the time of scanning isdeflected with the electrostatic deflector 325 and returned with theelectrostatic deflector 319 of the beam separator 323, deflecting aroundthe deflection pivot 335. The position of the deflection pivot 335 canbe adjusted by changing a ratio of amounts of deflection of thetwo-stage electrostatic deflectors 325 and 319. The position of thedeflection pivot 335 may be determined by simulation or by actualobservations as a value that can minimize the aberration. In otherwords, as shown in FIG. 3B, a ratio of the deflection sensitivities ofthe two-stage electrostatic deflectors 325 and 319 may be adjusted insuch a manner that the deflection pivot be located on the side of theelectron gun rather than the principal plane of the objective lens 313and at a position L between the position A where the coma aberration atthe time of deflection becomes minimal and the position B where thedeflection chromatic aberration becomes minimal, preferably at aposition C where the aberration becomes minimal.

The secondary electrons emitted from the sample are designed to becondensed with the objective lens 313 forming an magnified image in thevicinity of the main deflection plane of the beam separator 323. Thiscan make the deflection chromatic aberration substantially null which isgenerated at the magnified image by the deflection chromatic aberrationof the beam separator. As the secondary electrons which formed the imagein the vicinity of the principal plane of the beam separator is returnedtoward the direction of the optical axis with the electrostaticdeflector 319 of the beam separator, a bore dimension of the magnifyinglens 337 of the second stage can be made relatively small because theypass near the optical axis after passage through the beam separator evenif the sample is scanned by approximately 100 μm. It is necessary,however, that the length of the lower magnetic pole 341 of the objectivelens 337 in the direction of the optical axis be set to double or morethan double the bore dimension in order for the magnetic field leakedfrom the lens gap 339 to cause no occurrence of astigmatism of theprimary beams. Moreover, this can be prevented in a more secure way whenthe vacuum wall for the primary beams is made from permalloy. Aspermalloy is a ferromagnetic material, the magnetic flux generated atthe lens gap 339 and leaked from the lower magnetic pole 341 can bemagnetically shielded. The lens 337 may comprise an electrostatic lenswhich causes no rotation even if the lens adjustment is carried out.

Reference numeral 343 refers to an electromagnetic lens that can adjusta position of multiple beams and the direction of arrangement of thedetector by changing an amount of rotation without substantiallychanging the image-forming conditions of the lens having a long focusingdistance. Reference numeral 345 refers to the vacuum window having FOP(fiber optics plate) which is coated with a scintillator on the vacuumside. Reference numeral 347 refers to an optical lens for which a zoommechanism and an automatic focusing mechanism of a commerciallyavailable camera can be applied as it is without modification. Referencenumeral 349 refers to a PMT array for which a commercially available PMTarray with eight columns and eight rows of PMTs combined in one unit canbe used. The PMT array 349 can be used by superimposing it on an X-Ystage capable of moving in the direction normal to the optical axis andaligning the positions of optical signals from the multiple beams withthe positions of the PMTs. Alternatively, an eight-pole electrostaticdeflector may be mounted behind the magnifying lens 337 to align thepositions of the multiple beams on the plane of the vacuum wall 345. Theeight-pole electrode may be supplied with signals in synchronizationwith the scanning of the primary beams, thereby permitting the secondaryelectrons from the identical beams always to radiate the scintillator atthe same positions without relationship with the scanning position. Inaddition, astigmatism caused to occur on the scintillator plane can becorrected by sending signals for correcting astigmatism to theelectrode.

FIG. 3( b) illustrates the direction of the secondary optical system. Asshown in FIG. 3( b), the direction of scanning the sample by the primarybeams is expressed as reference numeral 327, which is parallel to thex-axis, and the direction of deflection on the sample with the beamseparator 323 is parallel to the y-axis for both of the electrostaticdeflector 319 and the electromagnetic deflector 321, as expressed asreference numeral 329. In the event where the direction of deflection ofthe beam separator 323 is set to the direction on the sample asindicated by reference numeral 329, the primary beams can be deflectedtoward the direction as indicated by reference numeral 331 when therotational amount 333 of the secondary beams with the objective lens 313is taken into account. As a result, the secondary beam is deflectedtoward the direction as expressed by 331 so that the secondary opticalsystem 331 is disposed in the direction 331.

As the focal depth of the lens 333 at the scintillator is deep enough,the blur in the beams on the scintillator plane does not increase evenif the amount of rotation of the secondary beam is changed. Therefore,the electromagnetic lens 343 can be omitted by using arotation-adjustable lens for the lens 337. Reference numeral 351 refersto a multi-aperture for adjusting a quantity of light which is disposedon the front side of the PMT array 349. At a portion near the opticalaxis, the intensity of the primary beams is so strong and an aberrationof an image of the secondary electrons is so small that the number ofsignals may become large. On the other hand, at a peripheral portionapart from the optical axis, the intensity of the primary beam is sosmall and an aberration of a secondary system is so large that thenumber of signals may become small. Therefore, the multi-aperture 351can be set to have a smaller aperture area at the portion near theoptical axis and a larger aperture area at the portion apart from theoptical axis. In particular, a crosstalk is small even if no aperture isdisposed outside because no detector is disposed adjacent to the end ofeach line and each row.

In FIG. 3, reference numeral 353 refers to a deflector for conducting adynamic correction; reference numeral 355 to an exciting coil of theobjective lens 313; reference numeral 357 to a sealing for separatingthe exciting coil from the vacuum portion of an electron beam apparatusin order to permit the exciting coil to be mounted in the atmosphere;and reference numeral 359 to an O-ring for the sealing.

As described above, the embodiment as illustrated in FIG. 3 can producea large beam current even if the beams are reduced to a smaller sizebecause the electromagnetic lens and the lens gap as well contract themultiple beams using the lens disposed on the side of the sample. Theconventional system has a great problem, however, such that, as themagnetic field is present on the sample, the beams emitted verticallyfrom the sample do not cross the optical axis so that the NA aperturecannot be disposed and, as a result, the crosstalk with adjacent beamsmay become large. In this embodiment, on the other hand, an image havinga high precision can be formed by mounting a small aperture in front ofthe detector in place of the NA aperture and by making a crosstalk withadjacent beams smaller.

Fourth Embodiment

FIG. 4 illustrates an electron beam system in which the sample isscanned by primary beams having a low resolution, but large beamcurrent, and an image of the secondary electrons is magnified on thedetecting plane with the magnifying secondary optical system and whichis provided with an aperture on the detecting plane in order to obtainan image of a high resolution. The primary beams (as shown on theright-hand side in the drawing) irradiate the sample S from thedirection inclined by approximately 30° with respect to the normal lineof the sample S. The aperture 403 is irradiated with the beams emittedfrom the electron gun 401, and a reduced image is formed on the plane ofthe sample plane 409 in association of the condenser lens 405 with theobjective lens 407. The cross-over 411 to be generated by the electrongun is formed on the principal plane of the objective lens 407 with theone-stage magnetic lens 405. The aperture 403 may be disposed in asingle or plural number.

The primary beams are deflected with the beam separator 413 leadingtoward the sample S passing through the trajectory 415 and forming thecross-over on the principal plane 417 of the objective lens 407. Thesample is subjected to raster scanning with the electrostatic deflector419 and the electrostatic deflector of the beam separator 413. Thesample S is applied with a negative voltage of several kv. For theobjective lens 407, there may be selected, for example, from the lens asillustrated in FIG. 1, a combination lens of a normal electromagneticlens and an electrostatic lens, or just an electrostatic lens. It isprovided, however, that, in the event where the lens as illustrated inFIG. 1 is selected, the NA aperture 421 cannot be disposed in thesecondary optical system. In other words, in this event, as the axialmagnetic field of the magnetic lens 407 is not zero or null on thesample plane, the secondary electrons emitted from the sample in thedirection of the normal line form no cross-over, i.e., they do not crossthe optical axis, so that no NA aperture can be disposed.

In the event where either objective lens other than the objective lensof FIG. 1 is selected, an accelerating electrical field for thesecondary electrons is formed between the sample S and the objectivelens 407 so that the secondary electrons emitted at a wide angle withrespect to the normal line of the sample plane is converged into asmaller size. Therefore, a high resolution can be achieved withoutdecreasing a detection efficiency of the secondary electrons, even ifthe NA aperture 421 is an aperture having a small dimension. As shown inFIG. 4, at least the principal light beams of the primary beam and thesecondary beam pass through different paths during the course betweenthe beam separator 413 and the sample plane S. This arrangement does notincrease the blur of the secondary beam due to the space-charge effectsof the primary beams. Moreover, as an image of the secondary electronsis formed on the main deflection plane of the beam separator 413 so thatno deflection chromatic aberration occurs at this portion. In addition,no chromatic aberration is caused to occur. In addition, no chromaticaberration will occur because the amount of electromagnetic deflectiondoubles the amount of electrostatic deflection.

This occurs because the deflection chromatic aberration caused by theelectromagnetic deflector of the beam separator 413 is equal in anabsolute value to a chromatic aberration of the electrostatic deflectors(the electrostatic deflector 419 and the electrostatic deflector of thebeam separator) and the directions of deflections are opposite to eachother. The image of the secondary electrons formed on the deflectionprincipal plane 423 of the beam separator is further magnified with themagnifying lens 425 forming an magnified image on the scintillatorcoated on the inner side of the vacuum window with the FOP disposed atthe central portion. Reference numeral 429 refers to a deflector fordynamic correction; reference numeral 431 to a light magnifying lens;and reference numeral 433 to a PMT array. The system of the presentinvention which is different to a great extent from the invention asshown in FIG. 3 resides in that the resolution of the primary beam hasto be improved whereas the resolution of the secondary beam has to beimproved for the aspect of the invention as shown in FIG. 4. In order toimprove the resolution of the secondary beam for this aspect of thepresent invention, accordingly, the image of the secondary electrons isformed on the deflection principal plane of the beam separator to removea deflection chromatic aberration at the time of deflection of thesecondary beam with the beam separator.

As described above, the embodiment as shown in FIG. 4 can form an imageof a high resolution while the beam size of the primary beam is beingkept magnified because the secondary electrons emitted from a smallregion of the sample can irradiate the detector by improving theresolution of the secondary optical system while the beam size of theprimary beam is being kept magnified. In the event where the scanning iseffected by the beam with a constant beam size while keeping the beamsize of the primary beam magnified, the beam current in a pixel can bemade smaller in proportion to the second power of pixel size, i.e.,(pixel size)², so that a throughput at a high resolution can bedecreased because the resulting signals are weakened at a slower rate ascompared with the conventional case where the beam current becomessmaller in proportion to the fourth power of pixel size, i.e., (pixelsize)⁴.

Fifth Embodiment

FIG. 5 shows an embodiment of the present invention 1-6. In theembodiment as shown in FIG. 5, neither the primary optical system northe secondary optical system are disposed vertically to the sample planeso that the deflection chromatic aberration at either optical axis canbe removed, but it is difficult to manufacture an optical system with ahigh precision. FIG. 5 illustrates an embodiment for an electron beamsystem that can manufacture a lens mount with a high precision bymounting either of the primary and secondary optical systems at a rightangle to the sample. More specifically, FIG. 5 shows an embodiment inwhich the primary optical system is disposed at a right angle to thesample or, conversely, the secondary optical system can be disposed at aright angle to the sample by mounting the electron gun on the right-handside of the drawing and passing the electron beams in the directionopposite to that indicated by arrows. The following description is maderegarding the embodiment as shown in FIG. 5 alone, in which the primaryoptical system is disposed at a right angle to the sample.

FIG. 5 illustrates an essential portion of the electron beam system ofthe embodiment according to the present invention 1-6. In FIG. 5,reference numeral 501 refers to an electron gun; reference numeral 503to a condenser lens; reference numeral 505 to an axial alignmentdeflector; reference numeral 507 to an trajectory of principal lightbeams of primary beams; reference numeral 509 to a beam separatorcontaining an electrostatic deflector 511 and an electromagneticdeflector 513; reference numeral 515 to an objective lens; referencesign S to a sample; reference numeral 519 to an amount of deflection bythe electromagnetic deflector 513; reference numeral 521 to an amount ofdeflection by the electrostatic deflector 511; and reference numeral 523to an trajectory of principal light beams of secondary beams.

In this embodiment, the electron gun 501, the condenser lens 503 and thedeflector 505 are disposed on one optical axis while the objective lens515 and the beam separator 509 are disposed on another optical axisapart from the above optical axis, thereby deflection the electron beamsto the center of the beam separator 509 with the deflector 505.

Suppose that a Z-directional distance between the deflector 505 and thebeam separator 509 is expressed as L. When the electrons emitted fromthe sample S are intended to be deflected with the beam separator 509 by3 a toward the right-hand side of the drawing, a deviation amount Dbetween the two optical axes can be expressed as D=La. Then, formula (1)below can be given on the basis of the relation of the amounts ofdeflections and formula (2) can be given from the condition for removingthe deflection chromatic aberration.

(i) Where the deflector 505 is an electrostatic deflector:

$\begin{matrix}{{\left( {{Deflection}\mspace{14mu} {amount}\mspace{14mu} 519\mspace{14mu} {of}\mspace{14mu} {primary}\mspace{14mu} {beams}\mspace{14mu} {by}\mspace{14mu} {deflector}\mspace{14mu} 513} \right) - \left( {{Deflection}\mspace{14mu} {amount}\mspace{14mu} 521\mspace{14mu} {of}\mspace{14mu} {primary}\mspace{14mu} {beams}\mspace{14mu} {by}\mspace{14mu} {deflector}\mspace{14mu} 511} \right)} = \alpha} & (1) \\{{2 \times \begin{bmatrix}{{{Deflection}\mspace{14mu} {amount}\mspace{14mu} 521\mspace{14mu} {by}\mspace{14mu} {deflector}\mspace{14mu} 511} +} \\{\left( {{{Deflection}\mspace{14mu} {amount}\mspace{14mu} {by}\mspace{14mu} {deflector}\mspace{14mu} 505};\alpha} \right) \times {u/L}}\end{bmatrix}} = \left( {{Deflection}\mspace{14mu} {amount}\mspace{14mu} 519\mspace{14mu} {by}\mspace{14mu} {deflector}\mspace{14mu} 513} \right)} & (2)\end{matrix}$

A ratio of the deflection amount 511 with respect to the deflectionamount 513 can be determined from the simultaneous equations of theformulas (1) and (2).

(ii) Where the deflector 505 is an electromagnetic deflector, theformula (1) above is the same as described above while the formula (2)is amended to formula (2)′ which can be read as follows:

$\begin{matrix}{{2 \times \left( {{Deflection}\mspace{14mu} {amount}\mspace{14mu} 521\mspace{14mu} {by}\mspace{14mu} {deflector}\mspace{14mu} 511} \right)} = {\quad\begin{bmatrix}{\left( {{Deflection}\mspace{14mu} {amount}\mspace{14mu} 519\mspace{14mu} {by}\mspace{14mu} {deflection}\mspace{14mu} 513} \right) -} \\{\left( {{{Deflection}\mspace{14mu} {amount}\mspace{14mu} {by}\mspace{14mu} {deflector}\mspace{14mu} 505};\alpha} \right) \times {u/L}}\end{bmatrix}}} & (2)^{\prime}\end{matrix}$

A ratio of the deflection amount 511 with respect to the deflectionamount 513 can be determined from the simultaneous equations of theformulas (1) and (2)′ above.

Each of the formulas (2) and (2)′ can be given from the condition ofremoving the deflection chromatic aberration by the following equation:deflection amount by the electromagnetic deflector=2×(deflection amountby the electrostatic deflector). It is provided herein, however, that agradual decrease of the deflection chromatic aberration by the deflector505 at a rate of 1/L with respect to the deflection chromatic aberrationof the beam separator is taken into account. In the formulas above,symbol “u” refers to a length between a conjugate point of the objectivelens 515 and the sample plane 517 and the deflector 505. The beamseparator 509 may comprise an electromagnetic deflector alone.

In the event where the electron gun is disposed on the right-hand sideof FIG. 5 and the electron beams advance in the direction opposite tothat indicated by arrow, the electron beam emitted from the electron gunis deflected with the beam separator 509 irradiating vertically thesample S and the secondary electrons emitted from the sample aredeflected with the beam separator 509 toward the center of the deflector505 having another optical axis parallel to the normal direction of thesample, thereby aligning with the other optical axis with the deflector.As described above, the embodiment of FIG. 5 can mount either of theprimary optical system or the secondary optical system at a right angleto the sample, thereby manufacturing a mirror mount having a highprecision.

Sixth Embodiment

FIG. 6 illustrates an embodiment according to the present invention 1-6which is directed to the method for detecting a defect of a sample byfocusing or focussing the electron beams emitted from the sample byirradiation of the sample and passage through the sample or reflectedfrom the sample or reflected before striking the sample (for example,electron beams striking a sample having a negatively biased electronmirror surface) on the detector plane with an image projection opticalsystem. In this method, there may be utilized a die-to-die process whichis carried out by conducting a comparison of the image to be inspectedwith a reference image for each die and a cell-to-cell process which iscarried out by conducting such a comparison for each cell. A die 601 onthe sample may be composed of a mixture of a region 603 which has to beinspected only by the die-to-die process with a region 605 which canalso be inspected by the cell-to-cell process.

The defect inspection may be carried out by acquiring an image of thesample for each stripe divided from a die or a cell while moving a stagecontinuously in a y-axial direction. In this case, a circuit for animage forming part may be different in some cases between a circuit forcarrying out a die-to-die comparison and a circuit for carrying out acell-to-cell comparison. Even if such a circuit would be identical toeach other, software for use with the circuit may be different from eachother in many cases. Further, it may require a certain duration of timeto fetch an image in a circuit for use with the die-to-die comparison orwith the cell-to-cell comparison and shift the fetched image from thecircuit for the die-to-die comparison to the circuit for thecell-to-cell comparison or vice versa. Therefore, it is less preferredto carry out such a shift procedure within one field. In other words,for instance, in the event where a pixel frequency is supposed to be 100MHz, it will require 10 ns or shorter for example to shift the imagesignals fetched in a circuit for the die-to-die comparison to a circuitfor the cell-to-cell comparison within one field or vice versa. It isextremely difficult, accordingly, to carry out such work.

In the present invention 1-5, in order to require no shift procedurewithin one field as described above, a stripe is divided in such amanner that the boundary lines of the stripes come into agreement witheach other for both regions, that is, the regions B and B′ where thedefect inspection is to be conducted by the die-to-die comparison andthe region A where the defect inspection is to be conducted by thecell-to-cell comparison. In the region A where the cell-to-cellcomparison is to be conducted, the x-directional width “a” of the stripe607 is set to be wider by several times a pitch of the cell. In theregions B and B′ where the die-to-die comparison is to be conducted, thex-directional width “b” of the stripe 609 is set to be as wide as adimension of the field, that is, an x-directional dimension equal to ascanning width of the beam (a beam size in the case of the imageprojection type). This can facilitate the shift procedure because theshift of the circuits within one field is no longer needed unlike in theconventional method.

Seventh Embodiment

FIG. 7 is a flowchart of manufacturing process for semiconductor deviceswherein the above mentioned electron beam apparatus is applied toevaluation of the wafers. An example of a device manufacturing processwill be described according to the flowchart of FIG. 7. Themanufacturing process of the example in FIG. 7 comprises the followingmain processes.

(1) a wafer manufacturing process 250 for manufacturing a wafer (or apreparing process for preparing wafers);

(2) a mask manufacturing process 251 for manufacturing masks requiredfor exposure (or a preparing process for preparing the masks);

(3) a wafer processing process 252 for providing any processing requiredfor the wafer;

(4) a chip assembling process 253 for cutting out those chips formed onthe wafer one by one so as to make them operative;

(5) a chip testing process 254 for testing the finished chips. Each ofthose processes includes some sub steps, respectively.

Among these main processes, the wafer processing process set forth in(3) exerts critical affections to the performance of resultingsemiconductor devices. This process involves sequentially laminatingdesigned circuit patterns on the wafer to form a large number of chipswhich operate as memories, MPUs and so on. The wafer processing processincludes the following sub-processes:

(1) a thin film forming sub-process for forming dielectric thin filmsserving as insulating layers, metal thin films for forming wirings orelectrodes, and so on (using CVD, sputtering and so on);

(2) an oxidization sub-process for oxidizing the thin film layers andthe wafer substrate;

(3) a lithography sub-process for forming a resist pattern using masks(reticles) for selectively processing the thin film layers, the wafersubstrate etc.;

(4) an etching sub-process for processing the thin film layers and thesubstrate in conformity to the resist pattern (using, for example, dryetching techniques);

(5) an ion/impurity implantation/diffusion sub-process;

(6) a resist striping sub-process; and

(7) a sub-process for testing the processed wafer. The wafer processingprocess is repeated a number of times equal to the number of requiredlayers to manufacture semiconductor devices which operate as designed.

FIG. 8 is a flow chart illustrating the lithography sub-process whichforms the core of the wafer processing process mentioned above. Thelithography sub-process includes the following steps:

(1) a resist coating step 260 for coating a resist on the wafer on whichcircuit patterns have been formed in the previous process;

(2) a step 261 of exposing the resist;

(3) a developing step 262 for developing the exposed resist to produce aresist pattern; and

(4) an annealing step 263 for stabilizing the developed resist pattern.Since the aforementioned semiconductor device manufacturing process,wafer processing process and lithography process are well known, andtherefore no further description will be required.

In the event where the defect inspection system according to eachembodiment as described above is used in the wafer inspection step (7)above for inspection of wafers, a defect can be inspected at a highprecision with a semiconductor device having a fine pattern, too, insuch a state in which an image of secondary electron beams is free fromdisorder. Therefore, a yield of products can be improved.

It is to be noted herein that a pattern evaluation method for evaluatinga pattern can be applied extensively to evaluations of patterns ofproducts including a defect inspection of samples such as, for example,photomasks, reticles, wafers, etc. and measurements for line widths,alignment precision, potential contrast, and so on.

FIG. 9 is a schematic representation showing an electron beam system Aof the embodiment of the present invention 2-1. As shown in FIG. 9, theelectron beam system A comprises a primary optical system (electron beamirradiation optical system) a1, a secondary optical system (imageprojection optical system) a2, and a stage part A3.

The primary optical system A1 may comprise an electron gun 1, acondenser lens 2, a square-shaped aperture 3, a condenser lens 5, adeflector 6, beam separators 7 and 8, an electrostatic deflector 9, anobjective lens 10, and an electromagnetic deflector 11 for MOLoperation. The secondary optical system A2 may comprise a secondmagnifying lens 19, a NA aperture 20, a FOP (fiber optic plate) 22, azoom-magnifying lens 23, and a detector 24. The stage part A3 may beprovided with a laser-moving mirror 14, a laser-stationary mirror 15, areflecting mirror 16, a beam splitter 17, and a laseroscillating-receiving machine 18.

With the construction as described above, the electron beam is emittedfrom the electron gun 1 and focused with the condenser lens 2. Thefocused electron beams then form a cross-over at a predetermined point 4on the side upstream of the square-shaped aperture 3. The electron beamsdiverging from the predetermined point 4 where the cross-over is formedare then irradiated uniformly onto the square-shaped aperture 3. Theelectron beams passed through the square-shaped aperture 3 are deflectedwith the beam separator while they are being focused with the condenserlens 5, forming a cross-over on the principal plane of the objectivelens 10. Moreover, the electron beam diverging from the square-shapedaperture 3 advances while being focused slightly with the condenser lens5 and then deflected with the beam separators 7 and 8, and they passthrough the objective lens 10 forming an image on the sample S.

The surface of the sample S may be divided virtually into stripes 26each having a 400-μm width W and arranged in a longitudinal directionparallel to the y-directional axis. The stripe 26 is further dividedvirtually into main field regions, each having an elongated shapeparallel to the latitudinal direction (the x-axial direction of FIG.10). The main field region is further divided virtually into subfields27, each having four 25-μm sides. In other words, the stripe 26 isdivided into sixteen subfields 27 along the width W thereof. An image isformed in a 25-μm unit of each of the subfields 27 by irradiation withelectron beams. For the electron beam system A according to thisembodiment, a dimension of the sample S corresponding to one pixel uponforming a two-dimensional image is 0.1 μm so that each subfield 27having four 25-μm sides corresponds to 250×250 pixels. Therefore, animage can be formed in a 250×250 pixel portion (6.25×10⁴ pixels) perunit.

If a pixel frequency is assumed to be 1 GHz, time needed per one pixelis 1 ns so that the time needed for 6.25×10⁴ pixels can be calculatedby: 1 (ns)×6.25×10⁴ (pixels)=62.5 (μs). In other words, one subfield isirradiated with the electron beam for the duration as long as 62.5 μsand the electron beam is then moved to the adjacent subfield 27,followed by irradiation the subfield 27 with the electron beam andrepetition of these operations thereafter. In the event, accordingly,where the main field 26 is divided along the stripe width W into sixteensubfields 27 in each row as shown in FIG. 10, the time needed forirradiation of all the subfields in each row will be 62.5 μs×16.Therefore, the speed for moving the stage 12 in the x-axial directionwill be 25 μs/(62.5 μs×16)=25 mm/s. It is to be noted herein, however,that the size of subfield is not limited to the above particular one,needless to say, and it may have approximately 512×512 pixels.

Information regarding the speed, acceleration and position of the stage12 can be measured by means of a laser interferometer and the currentposition and near-future positions of the stage 12 can be computed. Inorder to cause no moving of the image to be formed on the detector 24,the deflectors 7 and 9 are subjected to feedforward correction duringthe duration of time for which one subfield 27 is being irradiated withthe electron beam.

On the other hand, the secondary electrons emitted from the surface ofthe sample S (and transmitting electrons transmitting through the sampleas well) are magnified with the objective lens 10 and the magnifyinglens 19 to several tens of times, forming an image having a regionslightly larger than one subfield 27 on the inner side of the FOP 22.The secondary electrons are then converted into an optical image by thescintillator coated on the inner side of the FOP 22, i.e., by asintilation substance emitting light upon absorption of an energy of theelectron beam, and transmitted to the detector 24. Concurrently, voltageis applied to the inner side of the FOP 22 for accelerating thesecondary electrons with the object to heighten a sintilation efficiencyof the scintillator. It is to be noted herein that each fiberconstituting the FOP 22 is configured in such a manner that an index ofrefraction is adjusted to become larger at the central portion andsmaller gradually and continually as the positions are more distant fromthe central portion. At this end, the light passing from the exit sideis substantially parallel to the axial line of the fiber even when thesecondary electrons are sent to the FOP 22 at various angles. Therefore,the zoom-magnifying optical lens 23 disposed on the downstream side ofthe FOP 22 can transmit the irradiating light by approximately 100% tothe detector (for example, a plane detector such as CCD sensor, etc.),even if it is a lens having a large F number.

It is to be noted herein that the electron beams of the secondaryelectrons to be emitted from the subfield at the position apart from theoptical axis cause no aberration outside the optical axis by theelectromagnetic lens because the objective lens 10 and theelectromagnetic deflector 11 satisfy the conditions as MOL (movingobject lens). The principal electron beams for this subfield outside theoptical axis advance along the trajectory as indicated by line 28. Inother words, the main electron beams from the subfield outside theoptical axis are deflected in such a manner that they do not passthrough the predetermined point 21 where the cross-over has been formedand they cross the optical axis at the deflection principal plane of thedeflector 7 by means of the deflector 9. Then, they are deflected withthe deflector 7 so as to become parallel to the optical axis. Theconditions for the MOL, the deflector 9 and the deflector 7 are measuredin advance for all the subfields 27 and saved in a memory, and they areeach set to the electron beam system A before irradiation of each of thesubfields 27 with the electron beams.

On the other hand, the electron beams irradiated from the electron gun 1advance in a direction opposite to the trajectory of the secondaryelectrons along an trajectory nearby the trajectory as indicated by line28 because the deflectors 7 and 9 are each an electrostatic deflector.Each of the electron beams has a slightly different amount of deflectionbecause each has a different energy. In order to allow a correction ofthe difference of the amounts of deflection with the deflector 6,however, a correction amount is saved in a memory for each of thesubfields 27.

The two-dimensional image of the subfield 27 formed with the detector 24is saved in a predetermined memory at the position corresponding to theposition of each subfield 27. The magnifying lens 19 is shaped in atruncated form in order to exert no influences on the primary electronbeams. The order of forming the image of the subfield 27 is indicated byarrows in FIG. 10. The above description is directed to the case whereone pixel in the two-dimensional image formed corresponds to 0.1 μm on awafer. On the other hand, in the event where a mode is changed in orderto make the size of one pixel 0.05 μm (i.e., corresponding to a halfsize), the square-shaped aperture 3 is changed to a smaller aperture 29having a half dimension without basically changing the opticalconditions of the primary optical system.

The laser interferometer is arranged in such a manner that a laser lightgenerated from the laser oscillator 18 is divided with the beam splitter17 and one is sent to the laser-moving mirror 14 while the other is sentto the laser-stationary mirror 15 through the reflecting mirror 16. Thelaser light reflecting from the laser-moving mirror 14 overlaps with thelaser light reflecting from the laser-stationary mirror 15 through thereflecting mirror 16 and the laser lights interfere with each other. Theinterference of the laser light is received by the laser receiver 18,thereby computing the position, speed, etc. of the laser-moving mirror14 from a variation with intensity caused thereby. It is further to benoted herein that the laser-stationary mirror 15 can accurately measurethe position of the sample even if a relative vibration, a thermalexpansion, etc. could be caused to occur between the objective lens 10and the sample S because it is fixed to the outer magnetic pole of theobjective lens 10.

FIG. 11 illustrates examples according to the present inventions 2-3 to2-8 and is an magnified view showing a sectional right-hand portion onlywhen viewed from the optical axis of the axially symmetric objectivelens 10. The objective lens 10 has the structure in which the magneticgap occurring between the inner magnetic pole 31 and the outer magneticpole 32 is positioned facing the sample S and the electron beam iscondensed in a magnetic field which occurs in the magnetic gap. A focaldistance can be changed by changing an electric current passing throughthe coil 33. The feature of the objective lens 10 is dependent to theaxis Z (central lens axis) of the axial magnetic field distributuin B.

As shown in FIG. 12, the magnetic field distributuin B is not null atthe sample position (Z=0) and has a predetermined magnitude. As theposition in the Z-axial direction where the magnetic field distributuinbecomes maximal is located to the side closer to the sample S than theinner magnetic pole 31, the main lens plane of the objective lens 10 islocated closer to the sample S than the inner magnetic pole 31. As aresult, the axial chromatic aberration and the spherical aberrationincrease to a great extent. Moreover, the deflectors (coils) 37 and 38for carrying out MOL operations can be used as an axially symmetricelectrode by accommodating it in a ceramic case and coating the surfacethereof with metal. An aberration can be made smaller by applying apositive voltage to the axially symmetric electrode.

A differential value D_(B) regarding the axis Z of the axial magneticfield distributuin B is also indicated in FIG. 12. The differentialvalue D_(B) is a positive value on the side of the sample S and anegative value at the side of the inner magnetic pole 31. In otherwords, in order to effect the MOL operations, it is needed to form amagnetic field deflection in proportion to the differential value D_(B),and the deflector is divided into two deflectors 37 and 38, therebyforming deflection of a magnetic field having an inverse reference sign.The electric current for exciting the deflectors 37 and 38 isincorporated therefrom by mounting the hermetic seal 36 on the vacuumseal tube 39. The voltage to be applied to the axially symmetricelectrode functioning as a coil case is also supplied from the hermeticseal 36.

Moreover, as shown in FIG. 11, the principal light beam passage 28 ofthe electron beams by the MOL operations is deflected in the directionof the optical axis only by the action of the electrostatic lens of theelectrostatic deflector 9 and then deflected in a direction parallel tothe optical axis with the electrostatic deflector 7 for the beamseparator, thereby the light beams advancing on the optical axis. In theevent where the principal beams advance on the optical axis, the beamspass through the center of the NA aperture 20 so that the NA aperture 20can be disposed forming a projection image having a small aberration onthe scintillator plane 22 a of the FOP 22. More specifically, the mainfield is divided into subfields, and an trajectory of the electron beamsemitted from the center of the subfield for each field is controlled topass through the center of the NA aperture. Therefore, an aberration ofthe electron beams from the subfield distant from the optical axis canbe made smaller, like in the event of the subfield closer to the opticalaxis, by carrying out the MOL operations that allow a lens to be used asthe NA aperture, the lens being capable of causing a magnetic field onthe sample S, which could not be used conventionally as an objectivelens.

Further, the electron gun 1 is provided with energy of 4 keV when thescintillator plane 22 a is earthed because a voltage of −4 kV is appliedto the cathode. It is found that an amount of light in which thescintillator plane 22 a emits when one electron enters becomes anincrease function of a beam energy. The signal intensity can bestrengthened by applying a positive voltage of approximately +10 kV tothe scintillator plane 22 a. Moreover, in the event where the pixel sizeis changed to a ½-fold dimension or a double dimension, etc., the samedetector can be used if the square-shaped aperture 3 is changed and thezoom-magnifying optical lens 23 is magnified by a 2-fold or a ½-foldmagnification, etc.

FIG. 13 illustrates an optical system effective particularly in the casewhere an magnification ratio of the secondary optical system is madelarger. In this electron beam system, the primary electron beams aresent from the direction of 2.777 . . . α with respect to the normal line92 of the sample S and deflected by 2 a by electromagnetic deflectionand by a by electrostatic deflection with the beam separators 57 and 58,i.e., by a total deflection amount of approximately 3α (this value being2.777 . . . α, i.e., approximately 2.8α, in the event where the primaryelectron has 4.5 keV and the secondary electron has 4 keV), thereby theelectron beams vertically irradiating the sample S. The secondaryelectron beams are deflected by 2α with the electromagnetic deflectorand by −α with the electrostatic deflector so that they are deflected tothe left-hand direction in a total amount of α and they then strike thelens 69. In FIG. 9, the image of the secondary electrons of the sample Sare formed on the deflection principal plane of the beam separator sothat the deflection chromatic aberration, etc. by the beam separator iscorrected with the lens on the downstream side causing no occurrence ofaberration on the surface of the scintillator plane 22 a.

Moreover, in the case of FIG. 13, the secondary electron of the sample Sis arranged to form a sample image at the predetermined point 91 in thevicinity of the lens 69. This structure results in shortening of a focaldistance of the lens 69 and magnifying an magnifying ratio of the lens69 to a great extent. Moreover, a magnifying ratio by the objective lens60 is somewhat magnified, realizing a short mirror mount having twostages of lenses and a magnification of 100 times or more. It is notedherein as a matter of course that no chromatic aberration by the beamseparators 57 and 58 is caused to occur because the amount ofelectrostatic deflection is a −½-fold amount of electromagneticdeflection. At an upper portion of FIG. 13, an magnified view of onefiber of the FOP 72 is shown. The optical fiber is arranged such thatits central portion has a higher index of refraction and a peripheralportion has a lower index of refraction. Therefore, even if the electronbeams strike at a wide angle θ as shown in the drawing, the lightoutgoing from the exit can advance in a direction substantially parallelto the optical axis of the optical fiber by setting the length of theFOP by odd times the focal distance of the optical fiber. This structureof the optical fiber can collect substantially all optical signals withthe detector 74 even if the zoom-in optical lens 73 would comprise alens having a relatively large F number.

Moreover, in order to make the space-charge effect small, the primaryelectron beam is deflected with the deflector 56, thereby advancing at aposition apart by approximately 100 μm from the optical axis, that is,on an trajectory as indicated by passage 93, and returning to theoptical axis with the objective lens 60. This permits the primary andsecondary electron beams to pass at different positions in a distancebetween the beam separators 57, 58 and the sample, so that the spacecharge of the primary electron beam can prevent the secondary electronbeam from blur and deviating.

As shown in FIG. 13, for example, if the value α is set to approximately7° or greater, the electron beams of the primary optical system may beseparated from that of the secondary optical system by approximately26.6° or greater. This value is satisfactory.

The electron beam system or the pattern-delineating method for forming apattern according to the present invention 2-12 can be preferablyapplied to the method of manufacturing a semiconductor device as shownin FIGS. 7 and 8. More specifically, when the present inventions 2-1 to2-12 are applied to the inspection step 254 of FIG. 7, fine patterns canbe inspected with a high precision and stability, thereby it becomespossible to improve the yield of products.

Examples according to the present invention 3-1 will be describedhereinafter with reference to FIGS. 14 to 17. FIG. 14 illustrates anentire layout of an electron optical system which can be applied to apattern evaluation method according to the present invention 3-1. Theelectron gun may comprise the LaB₆ cathode 701, the Wehnelt 702 and theanode 703. The anode 703 constitutes a lens 704. As the LaB₆ cathode 701referred to herein, there may be used a prism-shaped single crystalhaving each side width of approximately 0.5 mm in which its tip portionis sharpened at a vertex of 60° to 90° in a conical shape and abraded ina hemispherical form having a radius of curvature of 15 to 40 μm. Thislens 704 can adjust an angle at which the electron beam is emitted fromthe electron gun. The electron beam with its discharging angle adjustedwith the lens 704 is focused with the condenser lens 707 forming animage on the NA aperture 711. Reference numerals 705 and 706 refer eachto an axis-aligning deflector.

The multi-aperture 708 is disposed at a position downstream of thecondenser lens 707 and the multi-aperture 708 in turn generates multiplebeams. These multiple beams are reduced in two stages with the reducinglens 712 and the objective lens 717 forming multiple beams each having abeam size of approximately 100 μm or smaller on the sample S. Referencenumerals 709 and 710 refer each to a deflector for aligning the axis ofthe NA aperture 711 with the reducing lens 712. These multiple beamsscan the sample S in two-dimensional directions with the scanningdeflectors 713 and 715 to evaluate a pattern formed on the sample S.

The characteristics of the multiple beams are needed to be evaluatedbefore evaluation of the pattern on the sample. For evaluation of themultiple beams, a marker formed on the same Z coordinates as the sampleis scanned with the multiple beams. The secondary electrons generatedfrom the marker are accelerated and focused with an objective lens, andthe focused secondary electrons are deflected with the beam separators715 and 716 to the left when looked at FIG. 14 and then detected withthe single secondary electron detector 714. This procedure can evaluateat least one characteristic selected from beam separation, beamintensity and beam resolution. For the evaluation of the beamseparation, there may be used a dot pattern composed of heavy metal dotsas indicated by reference numeral 727 on a flat substrate (see FIG. 15).Four different kinds of dots are shown in FIG. 15. Each separation ofthe dots is set to be satisfactorily larger than the maximum separationbetween the beams and a diameter of each dot is set to be smaller thanthe minimal separation of the beams. Therefore, images of the dotscorresponding to the number of the multiple beams can be formed withinformation of the beam separation by subjecting to two-dimensionalcanning with the multiple beams in the vicinity of one dot. The distancebetween the multiple beams can be measured from the images of the dots.

In order to measure the beam current, i.e., the beam intensity, for eachbeam, a Faraday cup as illustrated in FIG. 15 may be used. Above theFaraday cup 726 having an upper opening 726 b, an aperture 724 with thepositive electric power 725 is disposed. The beam current which does notstrike the aperture 724 is not measured. Only the beams passed throughthe aperture 724 is measured with an ammeter PA. The beam current can bemeasured for each beam when the radial dimension of the aperture 724 isset to be smaller than the beam separation.

For the measurement for the beam resolution, as shown in FIG. 17, theremay be used a slit in the form of a knife edge 731 b of a plate 731magnifying parallel to the x-axis, which has a width of a dimensionsmaller than the minimal beam separation in the y-axial direction and alength of a dimension larger than the maximum beam separation in thex-axial direction. As clearly shown in FIGS. 17 b and 17 c, the knifeedge 731 b of the plate 731 is disposed above the upper opening 726 b ofthe Farady cup 726, and a semi-circular opening 724 b seen from theabove of the Farady cup 726 is formed by the upper opening 726 b of theFarady cup cut off by the knife edge 731 b of the plate 731.

The knife edge-shaped slit 731 b is scanned crosswise with the multiplebeams. If the scanning amplitude is large enough, a signal wave form asindicated by reference numeral 733 can be obtained as a Faraday cupcurrent. Suppose that the beam separation obtained by projecting eachbeam onto the y-axis is set to be “dy_(m)” and a rise time for elevatingthe signal 733 from 12% to 88% at the rise portion of each stage isexpressed as “t”, the resolution Δyi for each beam can be computed bythe following formula:

Δyi=(t ₁ /t ₂)×dy _(m).

The beam size in the x-axial direction, Δxi, can also be computed byobtaining a similar signal wave form as follows:

Δxi=(t ₁ /t′ ₂)×dx _(m).

It is needed herein that the knife edge-shaped Faraday cup aperturehaving a length of a dimension larger than the y-axial beam separationfor the beam group as indicated by reference numeral 32 and the beamgroup as indicated by reference numeral 34 is scanned crosswise by thebeams.

The dots 728, 729 and 730 are set each to have a dimension larger thanthe radial dimension of the dot 727, as shown in FIG. 15. If the dotsare too small, the resulting signals become so small that it isdifficult to find them. Therefore, these larger dots 728, 729 and 730are used to confirm the beam positions and then the smaller dots 727 aresearched. If it would be found that the beams are not arranged asoriginally designed by evaluating the dots in the manner as describedabove, then they are arranged as originally designed by adjusting thelenses or deflectors. The evaluation is finished as they are foundoriginally designed. More specifically, if the beam separation is toowide, the adjustment can be effected by shortening the focal distance ofthe reducing lens. On the other hand, if the beam size is too large, thebeam size can be adjusted by re-alignment of the focus of the objectivelens, re-alignment of axes or re-correction of astigmatism. Further, ifthe beam intensity is lacking, the adjustment can be effected byincreasing the current of the electron gun. As the evaluation of theprimary beams is completed, the direction of deflection of the beamseparator is inversed and the secondary electron group is deflectedtoward the directions of the secondary optical systems 719 and 721.

In the sample S as there is a large difference between the primary beamand the secondary beam in which the primary beam has an energy ofseveral hundreds eV while the secondary beam has an energy of severaleV, it is necessary to simultaneously focus the primary and secondarybeams with the objective lens 717. In order to focus them in thismanner, the distance between the reducing lens 712 and the objectivelens 717 may be made longer than the distance between the objective lens717 and the first magnifying lens 719.

Theoretically, as the dimension of the former is set to be more thandouble the dimension of the latter, each of the primary and secondarybeams can meet the combining conditions by a relatively large landingenergy of the primary beams. More specifically, an image point of thesecondary electron with the objective lens can be focused at a positionclose to the first magnifying lens 719. The image of the secondaryelectrons magnified with the first magnifying lens 719 is furthermagnified with the magnifying lens 721 forming an image of the secondaryelectrons in front of the MCP 723. The secondary electrons of each beamare then multiplied with the MCP 723 and absorbed with the multi-anode740 converting into a voltage signal with the resistance 741. Thevoltage signal is then amplified with the multi-amplifier 742 and thenconverted into a digital signal with the A/D converter 743. Atwo-dimensional image is formed with the image-forming circuit 744 andthe image of each beam is linked together forming an image of thesample.

The pattern of the dots 730 is used for uniting the signal intensity ofeach beam. As the size of the dot 730 is set to be sufficiently largerthan the beam separation, the signal intensity is sufficiently large. Asthe signals obtained with the multi-amplifier 742 are each divided intothe signal of each beam, no confusion with the adjacent signals may becaused to occur. Uniting the signal amplitudes can be effected byadjusting a gain of the multi-amplifier 742.

In accordance with the present invention 3-1, the primary and secondaryoptical systems of the multi-beams can be evaluated independently fromeach other so that the pattern evaluation can be carried out with a highprecision by using the multi-beams as designed. An embodimentillustrative of the present invention 3-2 will be described withreference to FIG. 18.

EMBODIMENT OF THE INVENTION 3-2

FIG. 18 illustrates details of the electron optical system to be usedfor the pattern evaluation method according to the present invention3-2. The electron gun may comprise the cathode 801, the Wehnelt 802 andthe anode 803. The cathode 801 is welded to the tungsten filament 828for heating. The cathode 801 is heated by passing a current through thefilament 828, and a current is supplied to the electron gun. The threeelectrodes are set each to have a given voltage in order to formdiverging beams without forming a cross-over by the electron beamsemitted from the electron gun. It has been found apparent by simulationthat this results in the beam assuming a negative value for a thirdorder spherical aberration. It is found apparent likewise by simulationthat a false cross-over is formed behind the cathode when the trajectoryof the diverging beam is magnified in the cathode direction.

The diverging beam emitted from the electron gun is converged with thecondenser lens 806 forming a cross-over on the NA aperture 810. Themulti-aperture 807 is disposed beneath the condenser lens 806 and themultiple apertures 807 generate multiple beams. If the cross-over havinga dimension substantially smaller than the dimension of the NA aperture810 is formed at the NA aperture 810 or in the vicinity thereof, theelectron beams are not substantially blocked and substantially all thebeams pass through the NA aperture without being blocked. Moreover, asthe dimension of the NA aperture is set to be sufficiently larger thanthe dimension of the cross-over, no problem may occur even if the NAaperture does not strictly coincide with the position of the cross-over.Further, the aberration is determined by an angle of the aperturedefined by the cross-over dimension so that no problem with aberrationoccurs. Therefore, it is not needed to strictly set an allowance valuefor adjustment of lenses.

An image of the cross-over is formed with the reducing lens 811 at thez-coordinate position at which the aberration slightly above theprincipal plane of the objective lens 815 becomes minimal. It is to benoted herein, however, that the aberration is greater at the aperturedistant from the optical axis of the multiple aperture 807 than at theaperture closer to the optical axis thereof. An aberration may occur inthe cross-over in the vicinity of the principal plane of the objectivelens due to a difference between a spherical aberration of thecross-over to be formed with the electron gun and a spherical aberrationby the condenser lens 806 and the reducing lens 807. In accordance withthe present invention, as the cross-over to be formed by the electrongun has a negative spherical aberration, only an aberrationcorresponding to the difference between the two aberrations is caused tooccur.

Therefore, in the event where the beams pass through the aperturedistant from the optical axis of the multiple aperture 807, which exertssmaller influences than conventional ones, are arranged to cross theoptical axis thereof at the z-coordinate position where the aberrationis small at the principal plane of the objective lens, the difference inaberration from the beams passed through the aperture closer to theoptical axis thereof the multiple aperture 807 can be alleviated. Thescanning of the sample plane can be conducted by using the two-stagedeflectors composed of the electrostatic deflector 812 and theelectrostatic deflector inside the beam separator 814. The ratio ofdeflections between the two-stage deflectors may be set such that themain point of deflection is located at the position which is differentfrom the cross-over position and is located slightly above the principalplane of the objective lens and where the deflection aberration becomessmallest.

The secondary electrons emitted from the scanning point on the sample Sare attracted by an accelerating electric field formed by applying avoltage of approximately −4 kV to the sample and approximately +16 kV tothe axially symmetric electrode 129 disposed below the objective lens,and the attracted secondary electrons are then accelerated andcondensed. The secondary electrons emitted at an angle of +/−90° orsmaller with respect to the normal line of the sample plane pass throughthe objective lens in the form of a small beam. The secondary electronspassed through the objective lens are separated with the beam separator814 from the primary optical system and directed toward the secondaryoptical system 817. At this point, as the secondary electrons are madein the form of a very small beam, almost all the secondary electronsgenerated from the sample are led to the direction of the detectorwithout mounting the NA aperture. Moreover, in order to improve acontrast of signals, a small aperture may be disposed in front of eachdetector to prevent a secondary electron of the adjacent beam fromdeviating from an original course.

A secondary electron group corresponding to multiple beams striking thesecondary optical system 817 is treated with the magnifying lenses 818and 820 to enlarge an separation between the mutual electrons, formingan magnified image of the scanning position with the MCP 822. Thesecondary electrons multiplied for each beam with the MCP 822 areabsorbed with the multi-anode 823 and converted into a voltage signalwith the resistance 824, then amplifying and converting into a digitalsignal with the amplifier and the A/D converter 825. A two-dimensionalimage is formed by the image-forming circuit 826 and the evaluation ofdefect inspection and so on is conducted with the comparator 827.

In order to enable an evaluation of beam resolution power and so on withthe primary beam alone, a marker disposed at the z-coordinate positionidentical to the sample plane is scanned. The secondary electronsemitted from the marker are led to the single secondary electrondetector 813 by reversing the direction of deflection of the beamseparator 814. This permits an individual evaluation of each of multiplebeams. The deflectors 804 and 805 are disposed for axial alignment withthe condenser lens 806 and the multiple aperture 807, and the deflectors808 and 809 are disposed for axial alignment with the NA aperture 810and the reducing lens 811. The magnifying lens 818 is configured suchthat the outer lens shape is in a conical form so as to be readilydisposed closer to the beam separator. The deflector 819 is driven insynchronization with the scanning of the primary beam and the secondarybeam is arranged passing always through the center of the lens 820. Thedeflector 821 is driven in synchronization with the scanning and acorrection is made to enable the secondary electrons to irradiate theMCP 822 at its given position.

In accordance with the present invention 3-2, the primary beam may beevaluated for intensity, resolution, relative position, posture and soon before the secondary beam is introduced into the secondary opticalsystem. This enables an accurate adjustment of beams. Further, theprimary and secondary beams are not intercepted at the NA aperture sothat the beams each having a substantially equal intensity can beirradiated to provide secondary electron signals having an equalintensity.

An embodiment of the present invention 3-3 will be described hereinafterin more detail with reference to FIGS. 19 and 20. FIG. 19 is a schematicrepresentation illustrating an electron optical system to be used forthe pattern evaluation method according to the present invention 3-2. Anelectron gun composed of the single crystal LaB₆ cathode 901, theWehnelt 902 and the anode 903 is used under space-charge limitconditions to generate primary electron beams having a small shot noise.The deflectors 904 and 905 for axial alignment are disposed in a twostage to axially align the condenser lenses 906, 907 and 909 with themultiple aperture 910. The central electrode 907 of the condenser lensesis supplied with voltage from the positive high-voltage power source 908enabling focussing the beams with a low aberration. This results infocusing the cross-over images formed by the electron gun at the NAaperture 913 with a small aberration.

Further, a small aberration can be likewise realized even if thecondenser lens is replaced with an electromagnetic lens. For the beamspassed through an aperture close to the optical axis and through anaperture remote therefrom, the principal light beams pass through the NAaperture 913. The deflectors 911 and 912 are disposed below the multipleaperture 910 in a two stage, thereby enabling an axial alignment of theNA aperture 913 with the reducing lenses 914, 915 and 917. The centralelectrode 915 of the reducing lenses is supplied with a high voltagefrom the positive power source 916 forming a reduced image of themultiple aperture 910. The reducing lenses 914, 915 and 917 can form animage of the NA aperture 913 at a position close to the upper electrode921 of the objective lenses 921, 922 and 924. A spherical aberration canbe made smaller by subjecting the reducing lens to positive voltageoperations.

Moreover, a spherical aberration can be likewise made smaller byreplacing the reducing lens with an electromagnetic lens. Thisreplacement can make an aberration at a cross-over smaller and anaberration in respect of the reduced image of the multiple aperture 910smaller as well. The reduced image of the multiple aperture 910 isfurther reduced by means of the objective lenses 921, 922 and 924,forming multiple beams on the sample S. For the objective lenses 921,922 and 924, the central electrode 922 is supplied with a positivevoltage from the power source 923 to enable operations for causing alower aberration, and the lower electrode 924 can also be supplied witha positive voltage from the power source 925 to enable further reducingan aberration. The replacement of this lens with an electromagnetic lenscan achieve a lower aberration. The sample S is scanned with multiplebeams with the two-stage deflectors 918 and 919.

The secondary electrons emitted from the scanning point of the sample Sis accelerated by an accelerating electric field formed by a positivevoltage of the lower electrode 922 of the objective lenses 921, 922 and924 and a negative voltage to be supplied to the sample S from the powersource 927 and condensed smaller, then passing through the objectivelenses 921, 922 and 924 and striking the beam separators 919 and 920 bywhich they in turn are deflected toward the direction of the secondaryoptical system. In the secondary optical system, the image of theelectron beams is magnified by means of the first magnifying lenses 928,929 and 930 as well as the second magnifying lenses 932, 933 and 934,disposed behind the beam separators 919 and 920, forming an image of themultiple beams in front of the MCP 936. The conditions for forming animage of primary electrons may include forming the point 950 immediatelybelow the reducing lenses 914, 915 and 917 as an object point and, as amatter of course, forming an image point on the sample S. As thesecondary electron has a beam energy far smaller than that of theprimary electron, the image points of the secondary beams are formed inthe vicinity of the beam separators 919 and 920 under objective lensconditions as set equally to the conditions for focusing the primarybeams. The resulting image points of the secondary beams correspond tothe object points of the first magnifying lenses 928, 929 and 930.

In order to operate the first magnifying lenses 928, 929 and 930 asmagnifying lenses, it is needed to shorten a distance between the lenselectrode 929 and the object point. This condition can be met byselecting the case of making an angle of deflection of the beamseparators 919 and 920 and the case of sharpening the outer shape of themagnifying lenses 928, 929 and 930 in the form of a cone or a truncatedcone with an upper half circle of its vertex having a smaller diameter.In the former, however, the problem resides in that a deflectionchromatic aberration in the primary beam is so large that the primarybeam cannot be finely narrowed down. For this reason, the latter isadopted for this embodiment of the present invention.

More specifically, in this embodiment, the outer shape of the magnifyinglenses is arranged as a whole in the form of a truncated cone in such amanner that an outer diameter of the front electrode 928 is set to besmallest and an outer diameter of the central electrode 929 is set to besomewhat larger than that of the front electrode while an outer diameterof the rear electrode 930 is set to be largest. Further, in order toexert no influence on the passage of the primary beam, the lenses 928,929 and 930 are disposed closer to the object point close to the beamseparators 919 and 920. The secondary electron beams corresponding tothe multiple beams irradiating the MCP 936 are each multiplied, absorbedwith the multi-anode disposed close to the rear of the MCP 936,converted into an electric signal with the resistance 937, amplified,and converted into a digital signal with the A/D converter. Atwo-dimensional image is then formed with the two-dimensional imageforming circuit 939. The two-dimensional image is compared with patterndata 941 with the comparator 940 to effect an evaluation for defectinspection and so on. Reference numerals 931 and 935 refer todeflectors, respectively.

In order to raise a throughput by an electron beam, the greater thenumber of beams in the multiple beams the better is the throughput. Inthe embodiment of the present invention, the number of the beams can bemade greater by arranging multiple beams as indicated by referencenumerals 942 to 949, inclusive, in FIG. 20. In this embodiment, 22 beamsare formed within an area having a radius of 5.3 μm or smaller from theoptical axis, in which a minimal separation between the beams is set to2 μm and an separation between the beams projected in the y-direction isset to 0.5 μm.

A two-dimensional image can be readily formed by scanning the beams inthe x-direction. The process according to the present invention 3-3 cancarry out a pattern evaluation with a high throughput because pluralbeams can be formed at a position close to one optical axis.

The present inventions 3-1 to 3-3 can be used for the method formanufacturing a semiconductor device as shown in FIGS. 7 and 8. When thepattern evaluation method for the evaluation of patterns can be used foran inspection step of the manufacturing method of FIG. 7, even asemiconductor having a fine pattern can be inspected with a highthroughput resulting in an inspection of all numbers and improvements ina yield of products.

An example of the present invention 4-1 will be described with referenceto FIG. 21 which in turn is a schematic representation showing a systemto be used for the pattern-delineating method for forming patternsaccording to the present invention 4-1. An electron gun may comprise theLaB₆ cathode 451, the Wehnelt 452 and the anode 453. The cathode 451 canbe operated under space-charge limit conditions making a shot noisesmaller and further an edge roughness can be made smaller even if apattern is formed at a dose as low as approximately 1 μc/cm². Theelectron beams emitted from the electron gun are accelerated to 2.5 keVand transmitted to the square-shaped beam-shaping aperture 454. Thebeams shaped square form an image with the aperture 454 at the charactermask 459 with the shaping lenses 455 and 456. A cross-over is formed atan immediate point between the lenses 455 and 456 and the deflector 457is disposed at that position. The deflector 457 can shift a character ofthe character mask 459 or change a dimension of a variable shaping beam.Further, the blanking deflector 458 for turning on or off the emittingof the electron beams is disposed at an upstream position distant fromthe cross-over.

The beam patterned with the character mask 459 is restricted with the NAaperture 460 so as for the aberration to meet the specification valueand reduced with the reducing lens 461 and the objective lens 462 to adefined contraction ratio. The beam is then aligned and focused on thewafer 477. At this point, a positive high voltage of +12.5 keV isapplied to the wafer 477 so that the wafer 477 is irradiated withelectron beams having energy of +15 keV corresponding to the differencebetween the positive high voltage of +12.5 keV and the cathode voltageof −2.5 keV. As the electron beams having this energy transmitthroughout an entire thickness of 500 nm of a monolayered resist and cansensitize the resist, the monolayered resist can be used. Thehigh-voltage power source 476 can be adjusted to provide an optimal beamenergy for the monolayered resist as the resist varies with a thickness.The x-directional length of the scanning field is 1 mm. The magneticfields of the four-stage electromagnetic deflectors 463, 464, 465 and466 are superimposed on the magnetic field of the electromagnetic lens462 to provide a beam edge resolution of 0.05 μm on the wafer 477 byimplementing an aberration correction.

The beam position in the 50 μm subfield can be made to vary at a highspeed by using the electrostatic deflectors 478 and 479 disposed insidethe electromagnetic deflector. The deflectors 478 and 479 are arrangedsuch that the surface of the main ceramic body is partially coated withmetal as an electrode in order to prevent an eddy current. The wafer 477is chucked in a flat state with the electrostatic chuck 472. A patternis drawn by moving the y-stage 474 continually in one direction and thex-stage 475 stepwise for moving the stripes. In the event where apositive voltage of 12.5 keV is applied to the wafer 477, a positivehigh-voltage of approximately 10 keV is applied to the electrostaticchuck electrode 473. As the wafer 477 may have a layer which may causean element breakage when a high voltage is applied rapidly thereto, thepower sources 476 and 480 are controlled to maintain the difference involtage between the electrostatic chuck electrode 473 and the wafer 477at 2.5 keV and at the same time the voltage to be applied to the wafer477 is elevated or lowered at a rate of 100 V/sec or lower.

In order to measure the position of the wafer 477, the light transmittedfrom the laser oscillator 467, passed through the beam splitter 469 andreflected from the beam-moving mirror 471 and the light transmitted fromthe laser oscillator (light receiver) 467 separated from the beamsplitter 469 are sent to the reflecting mirror 468 and thelaser-stationary mirror 470. The two lights reflected with these mirrorsare caused to interfere with each other and a variation with theintensity is detected with the light receiver 467 to compute the speedat which the wafer 477 is being moved. The integration of this speed cancompute the position of the wafer 477. The laser-stationary mirror 470is attached to a pole piece of the objective lens 462 to measure therelative position of the mirror mount and the wafer 477 in most accuratemanner.

As the beam energy needed at the time of varying the dimension of thevariable shaping beam, selecting the character on the character mask oreffecting blanking is as small as 2.5 keV, it is easy to control theelectron beams at a high speed. On the other hand, the landing energycan be elevated to 15 keV by applying an accelerating voltage to thewafer so that the beam transmits throughout an entire thickness of amonolayered resist to sensitize the resist. Therefore, a throughput canbe improved and a cost-of-owner can be made smaller.

As described above, the pattern-delineating method according to thepresent invention 4-1 can readily control electron beams at a high speedin an upstream stage. On the other hand, a large energy can be providedby accelerating the electron beams in a stage before the wafer isirradiated with the electron beams so that the monolayered resist can beused on the wafer. Moreover, as a lens other than the objective lensuses electron beams having a small energy, an electrostatic lens can beused to form an electron optical system of a compact size and at a lowcost.

The following is a description regarding the present invention 4-2 withreference to FIG. 22 to FIG. 25. FIG. 22 illustrates an electron opticalsystem to be used for the pattern-delineating method according to thepresent invention 4-2. An electron gun may comprise the cathode 551 towhich a voltage of −2.5 keV is applied, the Wehnelt 552 and the anode553. The cathode 551 may be made of single crystal LaB₆ and can decreasea shot noise to ¼ or lesser as compared with the case of a ZrO/Wshottkey cathode, when the cathode 551 is operated under space-chargelimit conditions. Therefore, even if a pattern is formed with a smalldose, an edge roughness can be controlled at a low level. The electronbeams emitted from the electron gun is transformed into a square imageby passing through the square shaping aperture 554. The image is focusedon the character mask 559 with the lenses 555 and 558. The cross-over tobe formed by the electron gun is focused at the center of deflection ofthe deflector 557 for selecting a character with the lens 555, formingan image which in turn is further focused on the NA aperture 561 withthe lens 558 and then focused at a position close to the objective lens563 with the reducing lens 562.

The selection of the character mask 559 and the shift between thecharacter mask and the variable shaping beam are effected with theelectromagnetic deflector 557. Upon varying the beam size of thevariable shaping beam, the electrostatic deflector 556 is used. Forblanking the beam, the blanking deflector 566 and the NA aperture 561acting as a blanking aperture are used. An image by the variable shapingbeam or an image by the character mask 559 is formed with the reducinglens 562 and the objective lens 563 as a reduced image on the wafer 565.For the objective lens 563, there may be used an electromagnetic lens.By decreasing aberration by means of the objective lens 563 and theelectromagnetic deflector 564, a 1.6 mm width can be scanned. Foralignment within the subfields, a sub-field deflector 567 which is anelectrostatic deflector is used. In the drawing, reference numeral 560refers to a deflector for correction.

A description will be made regarding the pattern-delineating methodaccording to a first embodiment of the present invention 4-2 withreference to FIG. 23. The system of FIG. 22 can realize a throughput ata rate of approximately 10 wafers/hour, in the event where a number ofpatterns is small as in the case of forming a contact hole. In the eventwhere a large number of patterns are required, however, the system ofFIG. 22 can realize a throughput at a rate as many as approximately 3wafers/hour. Therefore, a majority of forming patterns for layers isconducted by ArF lithography. Now, a description will be madehereinafter regarding the case of forming patterns by electron beams ona total number of three layers comprising a gate layer and two contacthole layers.

In the contact hole layer, a probability at which a boundary line of astripe crosses a pattern is so low that attention is needed to be paidto the fact that a gate pattern does not cross a boundary line of astripe in the gate layer. In this case, an intersection of the gatepattern with the boundary line of the stripe can be avoided withoutshaping the stripes in an uneven form by making a stripe width variablewithin the range, for example, from 1.5 mm to 1.6 mm without using afull stripe width range of 1.6 mm. In this case, it is to be noted that,as shown in FIG. 23, a stripe width of each of a stripe divided by agate layer 571, a stripe divided by a first contact hole layer 572 and astripe divided by a second contact hole layer 573 is set to become equalto each other at the identical positions of the three layers whencounted from each end.

In FIG. 23, reference numerals 574, 575 and 576 refer each to a boundaryline of a stripe divided. As specifically shown in FIG. 23, a distanceof a pattern from the left-hand end to the boundary line 573 is designedto become equal among the gate layer 571, the first contact hole layer572 and the second contact hole layer 573. It is further to be notedherein that each width W1 of the first stripes from among the threelayers is set to be different from each width W2, W3, W4, et seq., ofthe second, third, fourth, et seq., when looked at FIG. 23 toward theright.

A description will now be made regarding the pattern-delineating methodaccording to a second embodiment of the present invention 4-2 withreference to FIG. 24. In this device, patterns can also be formed withelectron beams on a layer for forming a source drain, in addition to thegate layer and the contact hole layers. In the layer for forming thesource drain, the transistor characteristics may become poor if itsconnection precision is low, although the stripes are large. Therefore,an intersection of a stripe with a pattern has to be avoided in order toensure good transistor characteristics. FIG. 24 is an magnified viewillustrating a portion in the vicinity of a boundary of stripesaccording to the second embodiment of the present invention. In thedrawing, solid lines refer to stripe boundary lines in the source drainlayer, e.g., 582, 582′, 582″ and 582′″, and to patterns in the sourcedrain layer, e.g., 583, 583′, 583″ and 583′″. Broken lines refer tostripe boundary lines in the gate layer, e.g., 584, 584′, 584″ and584′″, and to patterns in the gate layer, e.g., 585, 585′, 585″ and585′″. Dot-chain lines refer to stripe boundary lines in the contacthole layer, e.g., 586, 586′, 586″ and 586′″. A pattern 587 in thecontact hole layer is indicated as a black dot because it is so small.Reference numeral 581 refers to a stripe boundary line in the eventwhere a stripe width of 1.59 mm is adopted in the source drain layer,which is determined from the substantially largest field of an electronoptical mirror mount of the electron beam system, however, theintersection of the stripe boundary line with the pattern can be loweredin the event where the stripe width is set to become smaller byapproximately 0.5 mm as indicated by solid line.

It is to be noted that the stripe boundary line in the source drainlayer is disposed projecting to the right as indicated by referencenumeral 582. This configuration results in order to avoid theintersection with the pattern 583. On the contrary, the stripe boundaryline immediately thereunder as indicated by reference numeral 582′ isdisposed projecting to the left. This configuration is arranged inassociation with a left-hand projection of the stripe boundary line 584′of the gate layer in order to avoid an intersection with a pattern 585′in the gate layer. Moreover, the stripe boundary line 582″ of the sourcedrain layer located immediately thereunder is disposed projecting to theleft as indicated by 582″ in order to avoid an intersection with thepattern 583′. Likewise, the stripe boundary line 582′″ of the sourcedrain layer located immediately thereunder is disposed projecting to theright. This configuration is arranged in association with a right-handprojection of the stripe boundary line 584′″ in the gate layer in orderto avoid an intersection with the pattern 585′″ although there is nopattern that has to be avoided.

The stripe boundary lines 584, 584′, 584″ and 584′″ in the gate layerare disposed in an irregular arrangement in the same direction as thestripe boundary lines 582, 582′, 582″ and 582′″ in the source drainlayer, as shown in the drawing. The stripe boundary lines 586, 586′,586″ and 586′″ in the contact hole layer are disposed in an irregulararrangement in the same direction as the stripe boundary lines in theother layers, as indicated by dot-chain lines in the drawing. In thethree layers as a whole, the x-directional and y-directional coordinatesbetween the stripe boundary lines are each set to assume a difference of1 μm or lesser.

A description will now be made regarding a summary of procedures fordetermining the stripe boundary lines as shown in FIG. 24. It is firstdetermined that each pattern is formed by electron beams in the gatelayer, the layer forming a source drain and the contact hole layer andpatterns are formed in other layers by ArF lithography. Then, a stripeboundary line 581 is temporarily determined in a layer where thepatterns are formed by the electron beams. The patterns 583, 583′, 583″and 583′″ are extracted, which may raise problems if they would crossthe temporary boundary line 581. A shorter length of projection of eachof these patterns from the temporary boundary line 581 (indicated bybroken line) is shaped into a convex form directed to either the left orthe right, A this time, it is to be noted as a matter of course that,for all stripes, a stripe width ranging from the boundary line of theconvex portion to the boundary line of the convex portion should notexceed a substantially effective main field width of 1.6 mm.

The convex and concave portions of the boundary lines of the stripeswhere patterns are drawn by electron beams are disposed elongating inequal directions among all the layers. Generally, it is sufficientenough in many cases if at least two layers coincide with each other. Inaddition to coincidence in the directions of elongation of the convexand concave portions of the stripe boundary lines, it is more preferredto limit a difference of a dimension (in this case, e.g., 1 μm) betweenthe x-coordinate and the y-coordinate of the stripe boundary lines ofeach layer. This limit can prevent worsening of precision in alignmentamong the layers.

A description will now be made with reference to FIG. 25 regarding athird embodiment according to the present invention 4-2. In thisembodiment, the contact hole layer and the gate layer are formed withpatterns by electron beams, however, device performance will worsen if aprecision of alignment among the layers is poor. In this embodiment, anattempt to solve this problem with delineation precision is made bydelineating the stripes in an inclined fashion, unlike convex andconcave arrangement for the stripe boundary lines as described above.

First, a pattern region is divided into stripes by a substantiallylarger field of an electron optical system to determine the boundaryline 141. This stripe boundary line 141, however, divides the pattern143, etc. The patterns may cause this problem if a precision of etchingbetween the stripes is +/−20 nm. Thus, in this embodiment, the stripewidth is shortened to 0.7 mm and a stripe boundary line is set asindicated by solid line as reference numeral 142. The stripe boundaryline 142 does not divide all the patterns except pattern 147. Therefore,this arrangement can greatly reduce a number of patterns that will bedivided by the stripe boundary line 142.

All of the stripe boundary lines of the layer where the alignmentprecision between the layers may become an issue are arranged in thesame manner as the stripe boundary line 142. For the layer where apattern intersects with the stripe boundary line 142 as in the case ofthe pattern 145, the stripe is provided with an overlap region 162. Inthe overlap region 162, the pattern 145 is divided into smallerpatterns, for example, nine smaller patterns 147 to 155, inclusive.Doses of the small-divided patterns upon pattern formation by the leftstripe 146 are set in this order: 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2and 0.1, while doses of the small-divided patterns upon patternformation by the right stripe 156 are set in this order: 0.1, 0.2, 0.3,0.4, 0.5, 0.6, 0.7, 0.8 and 0.9, respectively. A combination of the doseby the stripe 146 with the respective dose by the stripe 156 scores atotal of 1.0 for each small-divided pattern, that is, in such a mannerthat the other pattern is provided with the same doses.

The above configuration can solve almost all problems with a poorconnection precision and the issue involved in a lack of an alignmentprecision between the layers can be reduced to a great extent. It isprovided, however, that the measures regarding a connection failure canbe involved only in stitching between the stripes and are not applied toa failure of the subfields or a defect of connection between thesubfields. This is because a defect of subfield stitching can becorrected with a high precision, as compared with a defect in connectionof the stripes so that it should be dealt with by improvements inprecision. As described above, in the embodiment according to thepresent invention 4-2, the problem with a poor stripe connection can beimproved without worsening in the alignment precision among the layers.

A description will be also made regarding the present invention 4-3 withreference to FIGS. 26 and 27. FIG. 26 illustrates an electron beamsystem according to the present invention 4-3. A device is commerciallyavailable in which the cathode 651 with a ZrO/W spot-welded to atungsten filament is set to the shottkey shield 652. The anode 653 isprovided with an aperture, 100 μm in diameter, at a position distantfrom the optical axis, although having no aperture on the optical axis.The principal light beams passed through an aperture of the anode 653are adjusted with the electromagnetic lens 654 to form a cross-over infront of the reducing lens 655. A reduced image of the aperture of theanode 653 is formed below the reducing lens 655 with the lenses 654 and655 and the image is further reduced to approximately 1/100 on the maskwith the objective lens 656. The objective lens 656 is arranged to havean aberration of approximately 10 nm by means of the electromagneticlens with its lens gap disposed on the mask side forming a beam with abeam size of approximately 14 nm when the beam is conformed to adimension of the reduced image of 10 nm.

The mask surface can be supplied with gas for use in etching ordeposition from the gas inlet 660 or with H₂O gas having a largemultiplication rate of secondary electrons. A differential exhaustmechanism is provided in order that the mask chamber is not filled withsuch a reactive gas, thereby capable of discharging exhaust gas fromeach exhaust outlet to the rotary pump 661, the mechanical booster pump662 and the TMP pumps 663 and 664.

Further, in order to reduce an amount of those gases with the objectpenetrating into the mirror mount, the objective aperture 657 acting asa pressure limit aperture and a NA aperture is minimized to, e.g., 30μmφ in diameter, and maintains a pressure ratio in the order of fourdigits or larger between the inside and outside of the mirror mount. Theobjective aperture 657 can be finely adjusted in the XY direction withthe XY-alignment mechanism 674 accurately on the optical axis whilelooking at a SEM image.

The secondary electrons emitted from the mask are multiplied upon impactwith H₂O gas or other gases and converted into voltage through theresistance 668 after absorption by the aperture 657. The electric signalis then amplified with the amplifier 669 and introduced into the CRTmonitor 667 for brightness modulation, thereby forming a secondaryelectron signal for a SEM image. Simultaneously, the CRT monitor 667 issupplied with a signal from a deflection control current 666 forming apattern image 670 of the mask on the CRT monitor 667.

As the position of the black defect 671 is confirmed on the CRT monitor667, the scanning region 672 containing the black defect 671 isdetermined, and a chlorinated gas is introduced into the scanning regionto repair the black defect 671. On the other hand, in the event wherethe white defect 675 exists, a gas derived from a tungsten compound,e.g., W(CO), is introduced to scan the region 676 for deposition on thewhite defect.

The above description relates to the case where the mask 659 may be madeof chromium in a normal way. Where a material is SiO₂ as for a phaseshift mask, gas containing a fluorine such as, for example, SF₆, CF₄,etc. may be used for etching and a Si compound such as, for example,silane (SiH₄), TEOS (tetraethoxysilane), etc. may be used fordeposition. In the case where the mask is of a semi-transparent membranemade of molybdenum (Mo) a chlorinated gas or a fluorinated gas such as,for example, CCl₄O₂, CF₄, NF₃, etc., may be used for etching and a mixedgas composed of a molybdenum compound and a silicon compound may be usedfor deposition.

The gas passed through the aperture 657 is converted into ions uponimpact with electrons and led to the cathode side along the trajectory677. The ions pass straight without being curved almost thoroughly withthe electromagnetic lens 654 and blocked with the aperture of the anode653. Therefore, they do not attack the cathode 651.

A liquid or a solid may also be used as a substitute for the gas to beintroduced at the time of etching or deposition. In the case of aliquid, a repair portion is sprayed and coated by means of a spin coateror a jet printing mechanism and then irradiated with electron beams. Inthe case of a solid, pulverized superfine particles or nano-particlesare sprayed or shaped in the form of a solution in the same manner as inthe case of a liquid.

In another embodiment where secondary electrons are detected, as shownin FIG. 27, a positive voltage is applied to the aperture 657 as a NAaperture from the power source 681 and the secondary electrons emittedfrom the scanning point of the mask 659 may be accelerated andcondensed, thereafter passing through the aperture 657, leading by thebeam separator 685 toward the secondary electron detector 688 along thetrajectory 687 where the secondary electrons are to be detected, andforming a SEM image. If the voltage to be applied to the aperture 657 asthe NA aperture would be too high, it will be emitted. On the otherhand, if the voltage would be too low, secondary electron detectionefficiency may be worsened. It is therefore needed to determine anappropriate voltage by experiments. Moreover, a supply of gas may beceased to decrease a pressure of gas at the time of acquiring the SEMimage, thereafter applying voltage to the aperture 657.

As described above, the invention 4-3 can control unnecessary etchingand deposition to a satisfactory extent by changing the kind of gases orpressure at the time of obtaining the SEM image or at the time ofetching or deposition.

Moreover, the invention 3-1 to 3-3, inclusive, can be applied to themethod for manufacturing the semiconductor device as shown in FIGS. 7and 8. When these pattern evaluation methods according to the presentinvention are used for the inspection step of the manufacturing methodof FIG. 7, a semiconductor device having fine patterns can be inspectedwith a high throughput, enabling an inspection of all number of patternsand improving a yield of products.

1. An electron beam system comprising: an electron gun, an irradiatingoptical system, an electron beam-transmittable sample and animage-focusing optical system respectively disposed on one optical axis,wherein a cross-over image formed by the electron gun is focused at aposition adjacent to a principal plane of an objective lens in theimage-focusing optical system, an image of an aperture for determining asubfield is focused on the sample, electrons passed through the sampleis magnified by the objective lens to form an magnified image in frontof a rear magnifying magnification lens, and an magnified image isformed on a detector by the magnifying magnification lens.
 2. Anelectron beam system comprising: an electron gun for emitting an primaryelectron beam; a shaping aperture for shaping the primary electron beamto focus an image on a sample surface; an electromagnetic deflector forseparating electrons emitted from the sample from the primary electronbeam after passing through an objective lens, and a plural lenses formagnifying the electrons separation and focusing an image on a detector,wherein a cross-over image to be formed by the electron gun is focusedon a principal plane of the objective lens, and principal rays of aprimary beam and a secondary beam pass through different positions in adistance between the electromagnetic deflector and the sample surface.